Noun
APDU (plural APDUs)
(computing) Initialism of application protocol data unit.
APDU transmission via a contactless interface is defined in ISO/IEC 14443 -4. Source: Internet
Typically, the first APDU an NFC reader sends to your device is a "SELECT AID" APDU; this APDU contains the AID that the reader wants to talk to. Source: Internet