This document attempts to communicate the concepts outlined in the Web Payments space by using specific terms to discuss particular concepts. This terminology is included below and linked to throughout the document to aid the reader:

[PSD2] an account held in the name of one or more payment service users which is used for the execution of payment transactions. [Capabilities] An account is a store of value with a balance and a history of debits and credits that affect that balance
account provider
[PSD2] account servicing payment service provider: a payment service provider providing and maintaining the payment account from which the payer wants the specific payment transaction to be made
[PSD2] procedures which allow the payment service provider to verify the identity of a payment service user or the validity of the use of a specific payment instrument, including the use of its personalized security credentials. [ECB] a security mechanism for verifying: 1) the identity of an individual or other entity (including verification by means of a computer or computer application); and 2) the level of authority of that person or entity (i.e. the ability of that person or entity to perform specific tasks or activities).
[Proposed text by Evert] Requesting acceptance of a payment from a payer to a payee at the account serving payment service provider or other actor according to payment rules defined by the relevant payment scheme. [ECB] the consent given by a participant (or a third party acting on behalf of that participant) in order to transfer funds or securities.
[ECB] the process of transmitting, reconciling and, in some cases, confirming transfer orders prior to settlement, potentially including the netting of orders and the establishment of final positions for settlement
credit institution
[ECB] a company duly authorized to carry out banking transactions on a regular basis (i.e. to receive deposits from the public, carry out credit transactions, make funds available and manage means of payment)
An entity paying to receive goods, services, or other things of value; abstractly known as a payer.
electronic money institution
[ECB] a term used in EU legislation to designate credit institutions which are governed by a simplified regulatory regime because their activity is limited to the issuance of electronic money and the provision of financial and non-financial services closely related to the issuance of electronic money.
A person, organization, or software agent that is capable of interacting with the world.
four corner model
A payment scheme which includes the following stakeholders: the payer (also known as the Cardholder), the Issuer (who has a relationship with the Cardholder), the Acceptor and the Acquirer (which has a relationship with the Acceptor). The payment scheme defines the rules which apply to all parties; there are no limitations as to who may join the scheme, as long as the requirements of the scheme are met.
A set of information that can be used to identify a particular entity such as a person, software agent, or organization. An entity may have multiple identities associated with it.
invoked payment app
The selected payment app that the user agent has invoked (executed) and passed payment app input data.
[Merriam-Webster] a book containing accounts to which debits and credits are posted from books of original entry
An entity receiving payment for goods, services, or other things of value; abstractly known as a payee.
An entity that receives funds as required by a transaction.
An entity that provides a source of funds as required by a transaction.
[ECB] in a strict sense, a payment is a transfer of funds which discharges an obligation on the part of a payer vis-a-vis a payee. However, in a technical or statistical sense, it is often used as a synonym for transfer order
payment app
A payment app is a component able to process a payment request and return a payment response.
payment app input
Data provided to the invoked payment app by the browser. This data is likely to be a subset of the payment request API input (e.g., payment method, payment method data, and transaction specific data).
payment app response
Data provided by the invoked payment app to the browser.
payment instrument
A mechanism used to transfer value from a payer to a payee. Examples: Corporate Visa card, personal Visa card, a bitcoin account, a PayPal account, and an Alipay account. [PSD2] any personalized device(s) and/or set of procedures agreed between the payment service user and the payment service provider and used in order to initiate a payment order. [ECB] a tool or a set of procedures enabling the transfer of funds from a payer to a payee.
payment mediator
[EXPERIMENTAL] The payment mediator fulfills a number of roles: A payment mediator thus co-ordinates the flow of messages between the payee, payer, and selected payment app.
payment method
[EXPERIMENTAL] A way of paying. A system and set of rules for payments. A payment app may support one or more payment methods. For example, Visa, Mastercard, American Express, are payment methods.
payment method data
[EXPERIMENTAL] The data describing an instance of a payment method. For example, for the Visa payment method this might be the card primary account number (PAN), expiry date, and CVV.
payment method identifier
A string that uniquely identifies a payment method that a user can use to complete a transaction.
payment method specification
A payment method specification defines what payment method data is required in payment requests and payment responses for a particular payment method. It also lists the payment method identifiers that are defined for that payment method.
payment orchestrator
The payment orchestrator is the entity or entities (payer, payee or payment service provider) that are orchestrating the steps required to complete the payment flow.
payment order
[PSD2] any instruction by a payer or payee to his payment service provider requesting the execution of a payment transaction
payment processor
An entity that submits and processes payments using a particular payment instrument to a payment network. Examples: Stripe, PayPal,, Atos, FedACH.
payment request
A request from a payee to be paid. It contains the details of what to pay and how the payment can be made. How the payment can be made is specified as a list of payment method identifiers. The payment request MUST contain all of the payment method data required for each payment method identified in it's set of supported payment methods.
payment request API
The javascript API specified in the Payment Request API specification. This API can be used by merchants to trigger a payment flow in the user agent or by payment apps to register or update their information in the user agent.
payment request API input
Data provided by the payee's Web application to the browser via the payment request API.
payment request API response
Data provided to the payee's Web application by the browser after completion of the payment request API.
payment response
A response to a payment request (normally the result of processing by a payment app). The content of a payment response will be dependant on how the payment is being processed.
payment scheme
Sets of rules and technical standards for the execution of payment transactions that have to be followed by adhering entities (payment processors, payers and payees). Examples: Visa, MasterCard, Bitcoin, Ripple, PayPal, Google Pay, Alipay, Yandex money, ACH, SEPA. [ECB] a set of interbank rules, practices and standards necessary for the functioning of payment services.
payment service provider
A body executing payment services such as credit institutions, electronic money institutions, post office giro institutions, payment institutions, central banks other than when acting in their capacity as a monetary authority or carrying out other functions of a public nature, and government departments and local authorities, other than when carrying out functions of a public nature.
payee-initiated payment
Also known as a pull payment, a type of transaction where the payee initiates the funds transfer from the payee. A credit card payment is an example of a pull payment.
Activities surrounding and including a transaction (e.g., discovery of an offer, negotiation of terms, selection of payment instrument, delivery, etc.).
payer-initiated payment
Also known as a push payment, a type of transaction where the payer initiates the funds transfer to the payee. PayPal is an example of a push payment.
The regulator is responsible for monitoring some payments activities and enforcing legal requirements.
[ECB] the completion of a transaction or of processing with the aim of discharging participants� obligations through the transfer of funds and/or securities. A settlement may be final or provisional.
three corner model
A payment scheme including the following stakeholders: the payer (also known as the Card Holder), the Issuer (who has a relationship with the payer), the Acceptor and the Acquirer (who has a relationship with the Acceptor), but where the Issuer and the Acquirer are the same entity.
An economic exchange between a payer and one or more payees. An agreement, communication, or movement carried out between a buyer and a seller to exchange an asset for payment.
transfer order
[ECB] an order or message requesting the transfer of assets (e.g. funds, securities, other financial instruments or commodities) from the debtor to the creditor.
user agent
A piece of software that acts on behalf of the user.
a software service, providing similar functions in the digital world to those provided by a physical wallet, namely: This definition of wallet may expand in the future to include other items people find in physical wallets such as digital receipts, coupons, and identification.
web browser
A user agent that allows the user to render and view HTML documents, and navigate the World Wide Web.