Open Systems Interconnect (OSI) (OSI)

a seven-layer hierarchical reference interface and communications model sponsored by ISO, 1984, known as the OSI Reference Model: layer 7--applications, layer 6--presentations, 5--session, 4--transport, 3--network, 2--data link, 1--physical. This model is incorporated at the operating system level. The OSI model is used to develop interfaces and integrate two dissimilar systems (i.e., PCs and UNIX or UNIX and mainframes).

A standard description for transmitting data in a telecommunications network. OSI defines a framework for implementing protocols in seven layers: physical (1), data link (2), network (3), transport (4), session (5), presentation (6), and application (7).