Application Protocol Data Unit
(APDU) A packet of data exchanged between two application programs across a network. This is the highest level view of communication in the OSI seven layer model and a single packet exchanged at this level may actually be transmitted as several packets at a lower layer as well as having extra information (headers) added for routing etc.
Last updated: 1995-12-19
Application Protocol Data Unit ♦ Applications Development Manager
Try this search on Wikipedia, Wiktionary, Google, OneLook.