Skip to Content
ISO 50001Glossary

ISO 50001 glossary

ISO 50001 has its own vocabulary. Terms such as EnPI, SEU and energy baseline sound technical, but they are easy to understand. This glossary explains the core terms of ISO 50001:2018  in plain English. The official definitions are in chapter 3 of the NEN publication . Use this page as a reference when you read the requirements of the standard or the energy aspects page.

The terms on this page are based on ISO 50001:2018. Some abbreviations come from the English terms (EnPI, SEU, EnMS) and are used in the same way in Dutch practice.

A

Action plan

A document for each SEU or objective. It describes which measures you take, who is responsible, when it is done, what it costs and what it delivers. Action plans drive continual improvement in the EnMS.

Example: “Reduce compressor consumption by 20% by Q3 2026: leak detection (€3k, responsible: maintenance service, deadline Q2 2026), new variable-speed compressor (€40k, responsible: facility manager, deadline Q3 2026).”

B

Baseline

See energy baseline.

C

Continual improvement

The core of ISO 50001. You do not set a goal once and then reach it. You improve again every year: new objectives, new measures, better performance. Set out in clause 10 of the standard.

Difference from other standards: In ISO 9001, continual improvement concerns process quality. In ISO 50001 it concerns energy performance specifically.

E

EnMS (energy management system)

The Dutch term is energiemanagementsysteem, the translation of Energy Management System (EnMS). It is the combination of policy, objectives, action plans, procedures, roles, monitoring and reviews through which an organisation structurally manages and improves its energy use.

An EnMS is not software or a dashboard. It is a way of working, recorded in documents and carried out by people. ISO 50001 describes the requirements an EnMS must meet.

Analogy: An EnMS is for energy what a quality management system (ISO 9001) is for quality: a structure that ensures you keep getting better.

Energy baseline

A reference point for your energy performance, against which you measure improvements. You usually choose a recent year as the starting point (for example 2024). The baseline is set on the basis of historical data (at least 12 months).

Why normalise? If your production grows, your absolute consumption may rise while you are in fact more efficient per unit. That is why you correct the baseline for relevant variables: production volume, outdoor temperature, occupancy rate.

Example: A bakery sets its baseline at 800 MWh of electricity in 2024, at a production of 1 million loaves. If production grows in 2025 to 1.2 million loaves and consumption is 900 MWh, the normalised baseline is 800 × (1.2/1.0) = 960 MWh. Actual consumption (900 MWh) is below the normalised baseline: the bakery has become more efficient.

See the detailed page on the energy baseline for more detail.

Energy review

A thorough analysis of an organisation’s energy use. You map out: which energy flows come in (electricity, gas, fuel, heat), where they go, and which processes or systems are the largest consumers?

The energy review is mandatory (clause 8.4) and forms the basis for identifying SEUs and the energy baseline.

Example: A metal company carries out an energy review and finds: 35% compressors, 25% HVAC, 20% production ovens, 10% lighting, 10% other. That determines where the focus goes.

See the detailed page on the energy review.

Energy policy

A short document (maximum 1 page) in which top management sets out its vision for energy management. Required under clause 5.2. It contains at least:

  • A commitment to continual improvement of energy performance
  • A commitment to comply with laws and regulations
  • A promise to make information and resources available

The energy policy is not a marketing document but an internal management tool. See the detailed page on the energy policy.

Energy performance

The measurable result of your energy management: how efficiently do you use energy? Expressed in concrete indicators (EnPIs) compared with the energy baseline.

EnPI (energy performance indicator)

The Dutch term is energieprestatie-indicator, the translation of Energy Performance Indicator. A measurable value that expresses the energy performance of an organisation or system. The KPIs of your energy management.

Examples:

  • kWh per unit produced (production)
  • MJ per m² of floor area (office or property)
  • GJ per FTE (service organisation)
  • PUE (Power Usage Effectiveness) for data centres
  • Litres of fuel per 100 tonne-kilometres (transport)

EnPIs must be relevant, influenceable and measurable. You report them at fixed intervals (monthly or quarterly) and compare them with the energy baseline and your objectives.

See the detailed page on energy performance indicators (EnPIs).

H

HLS (High Level Structure)

The standard structure followed by all modern ISO standards, including ISO 50001, ISO 9001, and ISO 14001. All standards have the same 10 chapters in the same order.

Advantage: If you already hold another ISO certificate, you already know the structure. Chapter 4 is always about context, chapter 5 about leadership, and so on. Only the content differs per standard.

I

Internal audit

A periodic self-assessment of your EnMS. You check whether the system works as intended, whether procedures are followed, and whether your energy performance is improving. Required under clause 9.2. See the detailed page on the internal audit.

M

Management review

A periodic discussion by top management of the progress of the energy management system. Required under clause 9.3. The agenda items are fixed: EnPI trends, objectives, action plans, risks and opportunities, and decisions on adjustments.

O

Operational control

Making sure that day-to-day work is carried out in an energy-efficient way. Think of work instructions for operators, maintenance plans for installations, and purchasing criteria for new equipment. Set out in clause 8.7 of the standard.

Example: An operator starts the production line using an energy-efficient start-up procedure: first lighting on, then compressors, then the oven (not everything at once). This is in the work instruction and reduces peak load.

P

PDCA

Plan-Do-Check-Act. The improvement cycle that underlies all ISO management system standards.

  • Plan: Set objectives and action plans
  • Do: Carry out the plans
  • Check: Measure the results and carry out internal audits
  • Act: Adjust based on what you measure

ISO 50001 is fully built on the PDCA cycle.

R

Relevant variable

A factor outside your control that affects your energy use and that you must take into account when normalising your energy baseline. Examples: production volume, outdoor temperature, occupancy rate of a building.

S

SEU (significant energy use)

The Dutch term is significant energieaspect. A process, system or device that accounts for a substantial share of total energy use or has a large saving potential.

Criteria for identifying an SEU:

  1. High consumption (often above 10% of the total)
  2. Large saving potential (outdated equipment, inefficient process)
  3. High variability (fluctuates strongly, so it can be optimised)
  4. Large future impact (planned expansion or investment)

Rule of thumb: Your SEUs together should cover at least 70-80% of your total energy use.

See the detailed page on significant energy aspects (SEUs).

Scope

The boundaries of your EnMS: which locations, processes and energy flows are covered? You determine the scope yourself, but it must be logical and documented. The scope must not be so narrow that your largest consumers fall outside it.

T

TJ (terajoule)

The unit of energy use that the revised EED directive  uses to determine obligations. 1 TJ = 1,000 GJ = 1,000,000 MJ.

Conversion reference:

  • 10 TJ ≈ 2.8 million kWh of electricity
  • 85 TJ ≈ 23.6 million kWh of electricity

Do you consume more than 85 TJ on average per year? Then you are obliged to introduce an energy management system by October 2027. Do you consume 10-85 TJ? Then the EED audit obligation applies.

V

Improvement objective

A specific, measurable objective for improving energy performance. It must be SMART: Specific, Measurable, Acceptable, Realistic, Time-bound.

Example: “Reduce electricity consumption per unit produced from 12 kWh to 10 kWh by 31 December 2026.”

More information

Sources

Energy policy (clause 5.2)The audit process