1. The technique used by layered protocols in which a layer
adds header information to the protocol data unit (PDU) from
the layer above. As an example, in Internet terminology, a
packet would contain a header from the physical layer,
followed by a header from the network layer (IP), followed by
a header from the transport layer (TCP), followed by the
application protocol data.
2. The ability to provide users with a well-defined interface
to a set of functions in a way which hides their internal
workings. In object-oriented programming, the technique of
keeping together data structures and the methods (procedures)
which act on them.
