Looking for more information about the 9 August power cut?

See our interim technical report and other ESO resources.

Glossary of terms

Here you can find the meanings of abbreviations, acronyms, and terms that we use in the electricity industry.


AAHEDC - Assistance for areas with high electricity distribution  

ACER - Agency for the Cooperation of Energy Regulators

ACS - Average cold spell

AI - Artificial Intelligence   

ANM - Active Network Management 

ARA - Annual report and accounts  

Arduous Forecast - A forecast that assumes a generator variability and wind variability against a 1 in 20 and ACS demand forecast

AS - Ancillary Services 



BCA - Bilateral connection agreement  

BEGA - Bilateral embedded generation agreement  

BEIS - Department for Business, Energy and Industrial Strategy

BELLA - Bilateral embedded licence exemptible large power station agreement  

Bipole outages - A combined outage on two associated poles on an interconnector

BM - Balancing Mechanism  

BMU - Balancing Mechanism Unit 

BMRSBalancing Mechanism Reporting System  

BOA - Bid Offer Acceptance 

BS - Balancing Services 

BSAD - Balancing Services Adjustment Data

BSC - Balancing and Settlement Code  

BSSG - Balancing services standing group 

BSUoS - Balancing Services Use of System 


C&S - Contracts and Settlements Team 

CACM - Capacity allocation and congestion management

CACoP - Code Administration Code of Practice  

CBR - Contingency balancing reserve

CBSG - Commercial balancing services group  

CES - Commercial Engineering Services  

CDM - Customer demand management 

CF - Charging Futures 

CfD - Contract for Difference 

ChUG - Charging user group  

Clean Forecast - A forecast that uses data that is largely unadjusted

CM - Capacity Market 

CMN - Capacity Market Notices  

CSAT - Customer Satisfaction 

CUSC - Connection and Use of System Code  


DA - Day ahead 

Darkness peak - Peak evening electricity demand which coincides with lighting up in winter 

DCC - Demand connection code

DECC - Department of Energy and Climate Change

DER - Distributed Energy Resource 

DISBSAD - Disaggregated Balancing Services Adjustment Data

DN - Distribution network  

DNO - Distribution network operator  

DRC - Data Registration Code 

De-rated Generation Availability - Submitted generator data which has been reduced to allow for shortfalls and breakdowns, including imports 

De-rated Margin - The average excess of available generation capacity over peak demand, expressed in percentage terms

De-rating Factor - A percentage applied to notified availability data submitted by power stations to allow for short falls and breakdowns

DSO - Distribution System Operator 

DSR - Demand side response  

DTU - Demand turn up


E&R - Emergency and Restoration

ECIT - Extending Competition in Transmission 

EDL - Electronic dispatch logging

Electricity Forward Agreement - A contract calling for the delivery of and payment for electric power in a future period

EFC - Equivalent Firm Capacity 

EFCC - Enhanced Frequency Control Capability  

EFR - Enhanced frequency response  

EGBL - Electricity balancing guidelines

Embedded - Any generation which is connected directly to the local distribution network, as well as combined heat and power schemes of any scale

Emergency Assistance Service - The potential to change interconnector flows in an emergency situation to a more favourable security of supply position for GB

EMR - Electricity Market Reform  

ENA - Energy Networks Association 

ENC - European network codes  

ENCC - Electricity National Control Centre 

ENTSO-E - European Network of Transmission System Owners for Electricity

ERPS - Enhanced reactive power service  

ESO - Electricity System Operator  

ETO - Electricity Transmission Owner  

ETR - European Transparency Regulation

ETYS - Electricity Ten Year Statement  

EV - Electric vehicles  


FBSR - Future Balancing Services Roadmap 

FCA - Forward capacity allocation

FES - Future Energy Scenarios

FFR - Firm frequency response  

FR - Frequency response 


GBSQSS - GB Security and Quality of Supply Standard 

GC - Grid Code  

GCDF - Grid code development forum  

Generator capacity - The total capacity of all generators

GSG - CUSC governance standing group  

GTMA - Grid Trade Master Agreement

GW - Gigawatt


HSE - Health and Safety Executive

HVDC - High voltage direct current


Interconnector - Electric lines or other electrical plants based within Great Britain which convey electricity between Great Britain and another country or territory


JESG - Joint European stakeholder group  

JPC - Joint planning committee  


Kw - Kilowatt  

Kwh - Kilowatt hour  


LCDP - Large Combustion Plant Directive 

LDTEC - Limited duration transmission entry capacity  

Load - The energy demand experienced on a system

LOLE - Loss of Load Expectation


Margin - The difference between the level of demand and supply that is available to meet it

Maximum Generation Service - A facility that allows access to capacity which is outside of the generator's normal operating range in emergency circumstances for up to 2 hours

MBSS - Monthly balancing services summary

MFR - Mandatory frequency response  

MODIS - Market Operation Data Interface System  

MW - Megawatt 


NBM - Non Balancing mechanism unit 

NDP - Network Development Policy 

NETS - National Electricity Transmission System  

NGET - National Grid Electricity Transmission 

NGP - National Grid Property

NISM - Notification of Insufficient System Margin 

NOA - Network Options Assessment

NRAPMNegative Reserve Active Power Margin 

NTS - National Transmission System


Ofgem - Office of Gas and Electricity Markets

OPMR - Operating Planning Margin Requirement 

ORPS - Obligatory reactive power service


PAS - Platform for Ancillary Services 

Peak - The maximum power requirement of a system at a given time, or the amount of power required to supply customers at times when need is greatest

PGBT - Pre-Gate Balancing Transaction 

Pumped Storage - Used for converting large quantities of electrical energy to potential energy

PV - Photovoltaic




Restricted - An estimate of the demand after any Customer Demand Management has occurred

RDP - Regional development plan 

REMIT - Regulation on wholesale energy markets integrity and transparency  

RES - Renewable Energy Source 

RfG - Requirements for generators

RIIO - Revenue = Incentives + Innovation + Outputs  regulatory framework


SBR - Supplemental balancing reserve

SF - Scaling factor  

SO - System operator 

SO to SO - System operator to system operator  

SOF - System Operability Framework

SONAR - System Operator Notification and Reporting System

SOQ - Supply offtake quantity  

SQSS - Security and Quality of Supply Standards  

SSAT - Stakeholder satisfaction

STC - System operator Transmission owner Code

STOR - Short-term operating reserve  

STTEC - Short-term transmission entry capacity (firm access service)


TCMF - Transmission charging methodology forum  

TEC - Transmission entry capacity  

TERRE - Trans European Replacement Reserve Exchange 

TNUoS - Transmission Network Use of System  

TO - Transmission owner  

TOGA - Transmission outage and generator availability 

TRW Transmission reinforcement works  

TSD - Transmission system demand 

TWRTransmission works register


UCA - Unit cost allowance


VIP - Visual Improvement Provision


- Watt

WD - Within day

Weekday peak demand - The highest electricity demand expected/observed during each week expected between Monday and Thursday

Winter Peak Demand - The highest electricity demand expected/observed during the winter