Practical Engineering Maintenance Glossary
Clear, workplace-focused definitions for terms used in industrial maintenance, reliability, electrical systems, HVAC, steam, utilities and automation. Use the linked guides and calculators when you need more depth.
A–C
Availability
The proportion of time an asset is capable of performing its required function when needed. A common inherent-availability expression is MTBF ÷ (MTBF + MTTR). Use the MTBF, MTTR & Availability Calculator for worked calculations.
Bearing failure
Loss of a bearing’s ability to support load and permit controlled motion. Common contributors include incorrect lubrication, contamination, misalignment, poor installation and electrical damage. See Bearing Failure Causes.
CAPEX
Capital expenditure: money invested in assets or major improvements expected to provide benefit over more than one operating period, such as a new chiller, production machine or major retrofit.
Canonical URL
The preferred public URL for a web page when multiple URLs could show equivalent content. On this academy site, canonical URLs help search engines understand which HTTPS page should be indexed.
Condition-Based Maintenance (CBM)
Maintenance initiated because measured or observed condition indicates deterioration or a developing fault, rather than simply because a fixed time interval has elapsed.
D–M
Differential pressure (ΔP)
The pressure difference between two points. In facilities and process systems it is commonly used to assess filters, coils, ducts, pumps and flow restrictions.
FMEA
Failure Mode and Effects Analysis: a structured method for identifying how a function can fail, what the effects and causes may be, what controls already exist, and which actions deserve priority. See FMEA for Maintenance Engineers.
Failure mode
The specific way a required function is lost or degraded—for example, a motor fails to start, a valve leaks internally, or an AHU cannot maintain airflow.
5-Why analysis
A root-cause questioning technique that repeatedly asks why a failure occurred while requiring evidence at each step. It should not be treated as a fixed requirement to ask exactly five questions. See the 5-Why RCA guide.
HVAC
Heating, Ventilation and Air Conditioning: systems that control indoor thermal conditions, ventilation, air movement and often humidity and filtration.
kVA
Kilovolt-amperes, a unit of apparent electrical power. In balanced three-phase systems it is related to line voltage and line current by √3 × V × I ÷ 1000. Explore the Three-Phase Power Calculator.
kW
Kilowatts, a unit of real power representing the rate at which useful electrical energy is converted or consumed. For balanced three-phase loads, power factor is part of the real-power calculation.
LOTO
Lockout/Tagout: an energy-isolation control process intended to prevent unexpected energization, startup or release of hazardous stored energy during work. Approved site procedures and applicable legal requirements take priority.
MTBF
Mean Time Between Failures: average operating time between qualifying failures for a repairable asset over a defined period and failure definition. See MTBF Explained.
MTTR
Mean Time To Repair: average time required to restore an asset after qualifying failures, based on a clearly defined repair-time boundary. See MTTR Explained.
O–R
OPEX
Operating expenditure: recurring cost associated with running and maintaining operations, such as utilities, routine consumables, contracted maintenance and normal repairs.
Power factor
The ratio of real power (kW) to apparent power (kVA) in an AC electrical system. Lower power factor means more current is required for the same real-power transfer, all else equal.
PPM
Planned Preventive Maintenance: scheduled maintenance intended to reduce foreseeable failures and deterioration. A useful PPM task states exactly what to inspect, measure, clean, adjust or test and what acceptance condition applies. See the Professional PPM Checklist guide.
Predictive maintenance
A maintenance approach that uses condition trends, measurements or analytical models to estimate developing degradation and plan intervention before functional failure.
RCA
Root Cause Analysis: a structured investigation used to identify evidence-supported underlying causes and define corrective actions that reduce recurrence, rather than stopping at the visible symptom.
RPN
Risk Priority Number: a commonly used FMEA score produced by multiplying severity, occurrence and detection ratings. It can help organize discussion but should not replace engineering judgement or risk criteria.
S–V
Simple payback
The initial project cost divided by estimated annual financial savings. It is an easy screening metric but does not account for discount rate, financing, equipment life or changes in future costs. Use the Energy Cost & Simple Payback Calculator.
Steam trap
An automatic device used in steam systems to discharge condensate and non-condensable gases while minimizing loss of live steam under its intended operating conditions. See Steam Trap Fundamentals.
VFD
Variable Frequency Drive: an electronic drive that controls AC motor speed and torque by varying output frequency and voltage. See VFD Fundamentals.
Work order
A controlled maintenance record that defines requested or planned work and normally captures asset, task, priority, labor, parts, dates, findings and completion information for traceability.