AID (Application Identifier)

An Application Identifier (AID) is a unique code used in smart card and payment systems to specify a particular application or service on the card. Think of it as a digital label that tells the system which specific application—like a credit card, transit pass, or access badge—is being used. When a card interacts with a device, the AID ensures that the correct application is activated for the transaction or function. This identification helps securely and efficiently manage multiple applications on the same card, enabling smooth and accurate processing of different types of digital services.