Application Protocol Data Unit
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Application Protocol Data Unit(networking)
(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.
This article is provided by FOLDOC - Free Online Dictionary of Computing (foldoc.org)