An account information service provider (AISP) is a company permitted to connect to a customer's online payment accounts, with that customer's consent, and retrieve information such as balances and transactions. It is the firm; the activity it performs is an account information service, which is explained in full in the Account Information Service (AIS) entry.
The role was created by the European Union's Second Payment Services Directive (PSD2) and carried into UK law. An AISP can only look; it cannot move money. Because of that, PSD2 lets a firm that only provides account information be registered rather than fully authorised as a payment institution, though it must hold professional indemnity insurance or a similar guarantee. A firm that can start payments from the customer's account is a different type, the payment initiation service provider (PISP), and many companies hold both permissions.
Banks must let AISPs connect through secure interfaces and must apply strong customer authentication when the customer grants access. AISPs are among the main building blocks of open banking.