This glossary explains, in plain English, the e-invoicing terms UK businesses will meet before the mandate starts on April 2029. Where a term has a fuller entry, follow the link to our glossary pages.
Definitions marked "official" follow wording used in UK government documents. The others are our plain-English summaries.
A–C
Access Point (AP). A certified provider that connects you to the Peppol network and sends and receives documents on your behalf. Corners 2 and 3 of the four-corner model. See Peppol Access Point and How to choose one.
AS4. The secure messaging protocol Peppol Access Points use to exchange documents with each other. You will rarely need to think about it.
B2B, B2G, B2C. Business-to-business, business-to-government and business-to-consumer. The UK mandate covers VAT invoices, which the government says are typically issued for B2B and B2G transactions "though not for business to customer transactions". See B2B and B2G.
BIS (Business Interoperability Specification). Peppol's name for an implementation guide for a business process, such as billing.
Bridging software (official). A tool that links spreadsheets or other non-compatible records to HMRC's systems so a business can meet Making Tax Digital requirements.
BT- numbers. Business Terms in EN 16931, each identifying a data field. BT-10, for example, is the buyer reference. See Buyer reference and PO reference.
BR- rules. Business Rules in EN 16931 and Peppol that validation checks against. BR-CO-15, for instance, checks that the invoice total with VAT equals the total without VAT plus the total VAT. See BR-CO-15.
CII (Cross Industry Invoice). An XML syntax from UN/CEFACT. EN 16931 can be expressed in UBL or CII. See UBL vs CII.
CIUS (Core Invoice Usage Specification). A set of extra rules layered on EN 16931 for a specific community. Peppol BIS Billing 3.0 is a CIUS. Whether the UK publishes its own is not yet known. See CIUS.
Clearance model (official). "A government authority or approved third party validates and clears e-invoices prior to being issued to the customer." The UK is not using one. See Clearance vs decentralised.
Continuous transaction controls (CTC) (official). "A collective term for various real time digital tax controls". See CTC.
Credit note. A document reducing or cancelling an amount invoiced. It will need to be structured too. See Credit notes in Peppol.
D–F
Decentralised model (official). "E-invoice data is submitted through authorised software providers", with no central government hub. This is the UK's chosen model. See Decentralised model.
Digital links. Under MTD for VAT, the electronic transfer of data between software programs. Copy and paste does not count.
EAS code (Electronic Address Scheme). A code that says what kind of identifier a Peppol address uses. In Peppol's list, 9932 is "United Kingdom VAT number" and 0088 is "Global Location Number". See Peppol EAS codes.
EDI (electronic data interchange). Older, usually bilateral exchange of structured business documents. See E-invoicing vs EDI.
EDIFACT (official). A UN standard for EDI "approved and published by the United Nations Economic Commission for Europe (UNECE) in 1987."
E-invoice (official). "An invoice document that is issued, transmitted, and received in a structured format which allows for automatic electronic processing." A PDF is not one. See Does a PDF count?.
EN 16931. The European standard setting out the core data of an electronic invoice. UK public bodies must accept invoices complying with BS EN 16931-1:2017. See EN 16931 explained.
E-reporting. Sending transaction data, rather than full invoices, to a tax authority. France uses the term for its reporting regime. Not part of the UK mandate at launch.
Five-corner model (official). Builds on the four-corner model by "introducing the ability for businesses to share information in real time, or close to real time, with the government authority (who act as the 5th corner)." See Five-corner model.
Four-corner model (official). "An e-invoicing model where businesses exchange e-invoices through their service providers". Supplier, supplier's provider, buyer's provider, buyer. See Four-corner model explained.
G–O
GLN (Global Location Number). A GS1 identifier for organisations and locations, common in the NHS and retail. Peppol EAS code 0088.
Interoperability. The ability to exchange invoices with anyone, whichever provider each side uses. It is the main reason the UK chose a single network.
Invoice Response. A Peppol message from buyer to supplier saying an invoice has been received, accepted, rejected or queried. See Invoice response and MLR.
Making Tax Digital (MTD). HMRC's programme requiring digital records and software filing, for VAT since 2019 and for Income Tax since April 2026. See MTD and E-invoicing vs MTD.
Message Level Response (MLR). A technical Peppol message reporting whether a received document passed validation.
OpenPeppol. The non-profit association under Belgian law that governs Peppol.
P–R
Participant ID / Peppol ID. Your address on Peppol: an EAS code plus an identifier, such as a UK VAT number. See Peppol ID and Peppol IDs in the UK.
PDF/A. An archival PDF format. Some consultation respondents asked for it as a low-cost option. It is still a PDF, not structured data.
Peppol. The international network and specifications the UK announced on 23 June 2026 as "the core interoperability network for e-invoicing in the UK". See What is Peppol?.
Peppol BIS Billing 3.0. Peppol's invoice and credit note specification, a CIUS of EN 16931. See Peppol BIS Billing 3.0 UK guide.
Peppol Directory. A searchable list of registered Peppol participants. See Peppol directory lookup.
Real-time reporting (RTR) (official). "The process of reporting tax information to tax authorities as transactions are made." Not part of the UK mandate in 2029. See Will HMRC require RTR?.
Reverse charge. Where the customer, not the supplier, accounts for VAT, as in the domestic reverse charge for construction. See Reverse charge e-invoices.
S–Z
Self-billing. The customer raises the invoice on the supplier's behalf, by agreement. UK treatment under the mandate is not yet confirmed. See Self-billing.
Simplified invoice. A shorter VAT invoice allowed for smaller retail sales. Whether these are in scope is not yet confirmed. See Receipts and simplified invoices.
SML and SMP. The Service Metadata Locator and Service Metadata Publisher, the "phone book" services that tell a sender's Access Point where and how to deliver. See SMP and SML explained.
Structured data. Data in fixed, labelled fields that software can read without human interpretation. See Structured data.
UBL (Universal Business Language) (official). An "open standard for electronic business documents". The usual syntax for Peppol invoices. See UBL.
Validation. Automatic checks that an invoice meets the schema and business rules. Failed invoices are rejected. See Common Peppol validation errors.
VAT category code. A code on each invoice line saying how VAT applies, such as S (standard), Z (zero), E (exempt) or AE (reverse charge). See UK VAT category codes.
VAT gap (official). "The difference between the VAT theoretical liability, estimated using national accounts data, and actual cash receipts." HMRC put it at 6.6% (£12.1 billion) for 2024 to 2025. See E-invoicing and the VAT gap.
VAT invoice (official). "An invoice which must contain information required by the VAT Act." See VAT invoice requirements.
ViDA (VAT in the Digital Age). The EU package adopted in March 2025, including digital reporting for intra-EU trade from 1 July 2030. EU law, not UK law. See Selling to EU customers.
XML. The text format in which UBL and CII invoices are written. See UK Peppol invoice XML example.
What to do now
Bookmark this page. Most businesses will never need to touch an XML file, but knowing the terms makes software demos and supplier conversations much easier. Then work through the readiness checklist.