Useful Reliability and Maintenance Definitions

Dictionary for Reliability and Maintenance

We’d complied a list of useful reliability and maintenance definitions. It seems that maintenance terms are evolving, new terms are being created all the time, but of course, they are just new names for maintenance terms still in existence.

The definition of Maintenance is the act of maintaining, the state of being maintained, care or upkeep of machinery, the process of maintaining or preserving someone or something, the process of keeping something in good condition, the work of keeping something in proper condition.

Useful reliability and maintenance definitions
IDCON maintenance and reliability defintions

Browse our Maintenance Definitions in our Reliability and Maintenance dictionary for common maintenance terms used by professionals in the Reliability and Maintenance field. Do you have terms that you commonly use that aren’t included? Send us an email at [email protected] with the term and the definition and it may be added to the list.

Actuarial Analysis: Statistical calculation, especially of life expectancy.

Add-on Work: Work added to a maintenance schedule after the agreed upon cut-off time for the schedule.

Action Results Indicator: Key Performance Indicators used for measuring results of actions that directly or indirectly impact the financial performance of the company. 

Apprentice: An employee in a certified training program to become a craftsperson.

Asset: An accounting term for any physical thing owned by a plant, such as buildings, equipment, desks, software, computers, etc.

Asset Number: A number assigned to a particular asset in a plant; should be used for accounting purposes. Note: an asset number is different from an equipment location number. An equipment location number stays in the same location, whereas an asset number may move location.

Asset Replacement Value: The current accounting value of all combined physical assets in a plant.

Assessment (Reliability): A study comparing the Current Best Practices (CBP) with actual performance. The study assesses the effectiveness of processes in place.

Autonomous Maintenance: Maintenance processes driven by hourly workforce without management support or intervention. Learn More about Autonomous maintenance.

Autonomous Training: Training that is incorporated into the day-to-day work processes. The training is based on experiences and findings from the daily work and is then communicated on a regular basis.

Availability: Percentage of total hours (8,760/year) or scheduled operating time a system is available for production.

Backlog: Volume of all requested maintenance work not yet completed. Learn about Managing your Backlog.

Backlog (Approved): All maintenance work that is not completed but is approved for execution.

Benchmarking: The continuous, systematic search for and implementation of better practices that lead to improved performance. Benchmark your organization.

Bill of Materials (BOM): A document of all parts for an asset. Do you know the 7 steps to build a better BoM?

Breakdown: When a piece of equipment ceases to function (according to predetermined parameters).

Break-In Job: Work that changes a set schedule after an agreed upon cut-off time. 

Break-in jobs are either breakdowns or emotional add-on work.

Capital Work: Work done for improvements or betterments which will increase the value of assets.

Capital Spares: Spare parts that are depreciated (not expensed) in accounting books.

Charge Rate: The cost per hour of a resource cost for the company. Wages plus benefits. Benefits are usually around 35% of the salary in the US and 50-60% in Europe. Benefits include insurance, vacations, and other time off.

Component: A generic technical part. Many components make up equipment. The hierarchy is parts – components – equipment – systems. Illustration

Computerized Maintenance Management System (CMMS): A computer program or interfacing programs used to manage the maintenance function in a plant.

Condition Based Maintenance (CBM): Maintenance actions taken as a result of investigated condition of parts or components. The condition is measured or evaluated during programmed inspections of parts and components.

Condition Monitoring: All work performed in order to find failures early.

Consequence Of Breakdown (COB): The “cost” (not always measured in money) of a breakdown of equipment. COB is prioritized as follows: 

  • Environmental damage or safety hazard
  • Production loss
  • High cost (equipment life)

Continuous Improvement: Continuous improvement of existing practices resulting in improved performance.

Corrective Maintenance: All maintenance performed to correct a breakdown or failure.

Cost-Effective: When the monetary benefit exceeds the cost of implementing an improvement.

Craftspeople: People with professional skills in mechanical, electrical, or instrumentation maintenance. Many plants require skills in several of the skills mentioned.

Criticality: The criticality of a component, equipment, or system based on the consequence of breakdown.

Current Best Practice (CBP)The best way known to do something in IDCON’s Results Oriented Maintenance (ROM) philosophy. The future might reveal a better way of doing something and thus change the CBP. A CBP is equal to an element, which is the lowest level of detail in a Key Process.

Cut-off Time: Time when a schedule closes.

Defect (1): Damage on the final product that forces the plant to scrap the product or sell the product for a lower price.

Defect (2): A failure in a part or component.

Downtime: Time when a system is not producing product. Downtime includes scheduled and unscheduled downtime.

Downtime (Scheduled): When a system is down, and the downtime was documented as scheduled before the cut-off time.

Downtime (Unscheduled): When a system is down, and the downtime was NOT documented as scheduled before the cut-off time.

Element: In the IDCON assessment, a CBP is equal to an element, which is the lowest level of detail in a Key Process. It is the best way known to do something. The future might reveal a better way of doing something and change the CBP. Illustration

Emergency Work: Emergency work is a synonym of break-in work.

Equipment: An asset that performs a function, e.g., a motor coupling pump pumps water from point A to point B.

Equipment History: Documentation for all events such as repairs, modification, and preventive maintenance performed for a specific equipment.

Equipment Location: A physical location in the plant for a piece of equipment.

Equipment Location Number: A unique number assigned to an equipment location.

Equipment Reliability: Time, speed, and quality performance as it relates to equipment. In IDCON’s RORM philosophy, equipment reliability is the result of maintenance work.

Essential Care: A compilation of processes that will prevent failures from occurring. For example: lubrication, alignment, balancing, cleaning and operating procedures, adjustments, and installation procedures. Essential Care prevents failures (prolongs life of equipment).

Estimated Replacement Value: Estimated present value of assets. Shortened to ERV.

Failure: When equipment condition reaches an unacceptable level. Example: A motor may be running, but the temperature is 250°F (unacceptable).

Failure Code: A classification of a failure.

Failure Developing Period: The time elapsed between a failure and the breakdown. Illustration

Failure Mode: Any event that may cause a failure.

Failure Mode and Effects Analysis (FMEA): Analysis tool to identify failure modes and assign priorities to each failure mode based on cost and occurrences.

Failure Rate: An average of how often a component, equipment or system fails in a given time period.

Feedback: In maintenance, this term is most commonly used when referring to the written description of the work completed on a work order.

Fixed Time Maintenance (FTM): This tactic provides for scheduled overhauls or replacements of components, often based on the recommendation of the equipment vendor, general plant experience with similar components, or analysis of the maintenance history of an individual piece of equipment and its components. Note: Only 10-15% of all component types have a predictable failure rate. Cost-effective use of FTM is therefore limited.

Frequency of Inspection: The time period between a repetitive inspection. The inspection frequency should be based on the Failure Developing Period. Note: A rule of thumb is that the inspection frequency should be ‘Failure Developing Period/ 2.’

Gantt Chart: A bar chart (histogram) of scheduled tasks. Microsoft Project and timelines are examples of software using Gantt charts.

Gap Analysis: A rated comparison of Current Best Practices and actual performance.

Goal: Measurable results you wish to accomplish at a projected point in time.

Iatrogenic: In maintenance, this means failures induced by an organization’s own employees. Note: Iatros means physician in Greek, and -genic, meaning induced by, is derived from the International Scientific Vocabulary. Combined, of course, they become iatrogenic, meaning ‘physician-induced.’ Iatrogenic disease is then a disease caused by a physician.

Infant Mortality: Component failures occurring during early life of component (1-12 months).

Inspection: Any activity performed to find a failure or breakdown.

Inspection List: The printed list of an inspection route.

Inspection Route: Documented instructions for condition monitoring tasks sorted in an effective walking path through an area. Examples: paperhandheld

Inspector: The person doing the inspection routes. Note: This could be an operator, craftsperson, supervisor, engineer, or manager.

Key Performance Indicator (KPI): A measurement of process performance.

Key Process            

The key processes for IDCON’s Current Best Practice (CBP) assessment format are:

  • Leadership and organization
  • Preventive Maintenance
  • Planning and Scheduling
  • Shutdown Turnaround Management
  • Root Cause Problem Elimination
  • Technical Database 
  • Materials Management
  • Skills Development maintenance
  • Safety – Maintenance
  • Engineering Interface


Life Cycle Cost (LCC): Total cost for acquiring, owning, and disposing of physical assets. Includes direct operational and maintenance costs and indirect costs for lost production when the system fails.

Life Cycle Profit (LCP): The present value of all revenue the equipment has generated less the LCC.

Logbook: Usually refers to operations log for problems found during shift.

Logic Tree: A charting method for why-why analysis.

Management of Change (MOC): A process used to track and manage any physical or specification changes made to process related equipment in a plant.

Maintainability: The ease to maintain equipment.

Maintenance Meaning: Maintenance consists of corrective maintenance, preventive maintenance, and continuous improvement. Illustration

Maintenance Engineering: Maintenance Engineers work on design specifications of minor modifications, preventive maintenance documentation, problem identification and elimination, maintenance training, and maintenance technical database.

Maintenance Management: Maintenance management is the collective term for describing the management process of leadership and organization, planning and scheduling, preventive maintenance, condition monitoring, execution of maintenance repairs, recording, root cause failure analysis, spare parts management, and management of technical data supporting the processes above.

Maintenance Opportunity: (See Maintenance Window)

Maintenance Planning: (See Planning)

Maintenance Prevention: All actions performed to prevent failures. Lubrication, alignment, balancing, installation and equipment design, operating procedures, detailed cleaning, adjustments, fixed time replacements, and filtration. Note: Maintenance prevention and condition monitoring are the two components of preventive maintenance.

Maintenance Window: Defined time slots when maintenance can be performed on equipment without disturbing production.

Mean Down Time (MDT): Average time equipment is down (for any reason).

Mean Time Between Failures (MTBF): Total calendar operating time divided by number of failures.

Mean Time To Repair (MTTR): Average Repair time for component.

Mean Wait Time (MWT): All time during downtime that isn’t repair time. MDT=MWT + MTTR.

Mission Statement: Summarizes how to achieve a vision.

Model Work Order: (See Standard Job Plan)

Non-Destructive Testing (NDT): Any material testing that doesn’t destroy material. During the testing process. Note: Usually we think of Ultrasonic Thickness Testing. Also included in NDT is usually dye-penetrant testing, x-ray testing, and electrical resistance testing. Vibration, thermography, look, listen, feel, smell, winding test, etc. are not included since they are testing components and equipment, not material.

Non-Scheduled work: (See Unscheduled Work)

Objective Condition Monitoring: Preferred over Subjective Condition Monitoring. Objective methods are, for example, vibration analysis, ultrasonics, and temperature, pressure, voltage, and ampere readings. Subjective inspections are look, listen, feel, and smell.

Off-line: Downtime for a component or system without affecting production. Note: If production is down, it’s considered an outage or Shutdown/Turnaround.

Oil Analysis: Testing of oil in order to find failures early

Operate To Breakdown (OTB): A maintenance strategy which operates equipment until breakdown. A maintenance strategy which sometimes can be the most cost effective. Note: OTB is used when the consequence of failure is small enough that the benefit of preventing or finding failures early is more costly. OTB will be the fact for failures that occur randomly and have no Failure Developing Period.

Outage: A shutdown/turnaround that affects the whole plant for more than 16 hours.

Overall Production Efficiency (OPE): 

The product of %Quality x %Speed x %Uptime for a production line.

Overall Reliability: (See Production Reliability)

Parts: (See Spare Parts)

Planned Job

A planned job includes: 

  • The person planning the job verifies the scope of the job.
  • Lifting equipment, tools, parts, material, and personnel. Equipment needed to do the jobs are identified and allocated.
  • Skills needed are identified.
  • A description of job steps is documented.
  • Lock-out/Tag-out and other safety requirements are identified.
  • Necessary technical documentation is available.
  • Craftspeople are part of the planning process.
  • Estimated job duration by skills and the number of people needed for the job.
  • Required permits available.
  • The cost of each job is estimated.
  • Define physical and environmental constraints.

Planning: The process of determining the resources, methods, and processes needed to perform maintenance work efficiently and effectively. Note: Planning is different from scheduling. The short definition of planning is to decide what, how, and time duration.

Predictive Maintenance: A synonym of Condition MonitoringNote: IDCON doesn’t use this term because it is often referred to as simply Vibration Analysis. There are many other condition monitoring tools besides vibration analysis.

Preventive Maintenance: Essential care combined with fixed time maintenance. Both essential care and fixed time maintenance prevent failures, while Condition Monitoring only detects failures early.

Priority: The assigned importance of a maintenance job.

Priority Code: The importance of a maintenance job is defined by a priority code. A priority code represents a deadline for when the maintenance job must be completed.

Priority Guideline: Agreed upon guidelines for assigning a priority to maintenance work. 

Proactive: Actions that are planned and scheduled and executed before a breakdown occurs. Includes maintenance prevention activities.

Problem: Any issue that can be improved in a cost-effective manner.

Process: A work system that is documented, executed, and measured.

Process Reliability: Time, speed, and quality performance as it relates to manufacturing process.

Production Reliability: The product of process and equipment reliability.

Purchase Order (PO): The document sent to a supplier to order parts, services, material, or machines.

Reliability Centered Maintenance (RCM): A maintenance philosophy which is heavily designed by engineers supported by sound theoretical practices. Note: No known plant has been able to implement a full RCM strategy. It is often a very complicated theory for simple common-sense actions. RCM has a given place in the specification phase when designing new equipment. (IDCON’s opinion).

Reliability (Equipment): The product of %Quality x %Speed x %Uptime as it relates to equipment.

Reliability (Process): The product of %Quality x %Speed x %Uptime as it relates to the process (operation of equipment).

Reliability (Production): The product of process reliability and equipment reliability. Measured by %Quality x %Speed x %Uptime.

Repair: Any activity intended to bring a component, equipment, or system back to a specific condition.

Repetitive Work: Work that is often repeated in the plant. Repetitive work should have Standard Job Plans.

Results: Financial outcome of one or several actions.

Results Indicators: Global Key Performance Indicators measuring results directly impacting the financial performance of a plant.

Rework: All repairs that must be done again due to a poor repair the first time. Note: A combination of poor planning and scheduling. Usually due to lack of skills, material problem, missing spare parts, or not enough time assigned to do a precision job before starting equipment again.

Results Oriented Maintenance (ROM): Maintenance Philosophy developed by IDCON, INC.

Root Cause Failure Analysis (RCFA): A systematic way to collect select, analyze, and solve failures.

Root Cause Problem Elimination (RCPE): A systematic way to collect select, analyze, solve, and eliminate a problem. (An IDCON CBP Key Process).

Safety: The result of all actions executed to prevent personal injuries.

Service Factor: A key performance indicator for the storeroom measuring the % of times the correct quantity of the correct part is received when requested. Note: If the service factor falls below 95%, maintenance people begin to lose confidence in the storeroom’s ability to supply the correct parts and materials when needed. Usually result in growth of “unofficial personal stores” at frontline level.

Scheduled Job: A job put on the schedule before the cut-off time. Specific people, start time, and end time is documented.

Scheduling: The process of determining which jobs get worked on when and by whom based on the priority and resource/equipment availability. Note: this process should take place before the job is executed. (See Break-In Job). Scheduling short definition is when and who.

Scheduling Compliance: A KPI that measures the sum of add-on jobs and jobs on the schedule but not completed OVER the jobs on the schedule before cut-off time.

Shock Pulse Measurement (SPM): A Condition Monitoring Tool measuring the shock pulse in rotating equipment. Note: Shock pulse is the pressure wave generated through materials when two materials hit each other. A vibration wave will be generated by the shock pulse.

Shutdown: Scheduled or unscheduled downtime for a system or plant area.

Source: An event that triggers a failure. Illustration

Spare Parts: All machine parts, materials, and supplies that may be required to repair an asset.

Standard Job Plans: A documented plan for a type of job that can be used repetitively. 

Sub process: A process with a lower hierarchy than a key process in IDCON’s CBP material. Illustration

Subjective Maintenance: Look, listen, feel, and smell.

System (1): A combination of equipment dependent on each other to complete a production task.

System (2): Can refer to a computer software, a work system, or production system.

Terotechnology: Maintenance management and technology. A term often used by universities in the UK.

Total Productive Maintenance (TPM): A maintenance philosophy. TPM is usually profiled for strong operator involvement in equipment care.

Tradesperson: (See Craftsperson)

Tribology: The science and technology of interacting surfaces in relative motion, including the study of lubrication, friction, and wear.

Tribological Wear: Wear that occurs as a result of relative motion on the surface.

Turnaround: (See Shutdown) Term usually used in steel, alumina, and mining industry.

Unplanned Maintenance Work: A maintenance job where necessary planned activities are incomplete before job is scheduled. Planning should always be done before scheduling.

Unscheduled Maintenance Work: Work added to the schedule after the cut-off time.

Uptime: Opposite of Downtime. Time when a component, equipment, or system is producing product. Note: The component, equipment or system may produce defective product or at a slower speed than usual.

Vibration Analysis: A Condition Monitoring tool measuring the vibration in equipment.

Vision Statement: Summarizes what an organization (or individual) wants to achieve in the future. A vision must be supported by a mission statement and a goal.

Why-why Analysis: A problem-solving method which forces the problem solver to break down and analyze different possible causes as to why a problem occurred.

Workload: All work in the approved backlog. Can be measured as follows: The sum of estimated hours in the approved backlog divided by the craftspeople available for a particular area or supervisor. Best is to trend this number over time. A well-managed maintenance area has about 2-4 weeks of workload.

Work Order: An approved work request.

Work Request: A request to do maintenance work.

At IDCON, we understand the pressure you face trying to build a reliable plant.
We provide side-by-side reliability and maintenance consulting and training designed to keep your equipment running.

For over 45 years, we’ve partnered with 100s of manufacturing plants around the world to eliminate the costs and the pressure caused by unreliable equipment. And we’d love to do the same for you.

Contact us today to see how we can help you keep your plant running.

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Picture of Torbjörn Idhammar

Torbjörn Idhammar

President & CEO, IDCON Inc. Reliability and Maintenance Consultant

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