1. The unit of information transferred by a message switching system. Messages may be of any length, from a few bits to a complete file, and no part of a message is released to its final recipient until all of the message has been received at the network node adjacent to the destination.

2. Another name (deprecated) for packet. The distinction between packet and message is valuable, since it refers to whether or not a partial transmission of a complete document can occur; a packet switching system may allow this whereas a message switching system may not.

3. See Shannon’s model (of a communication system).

4. A specially formatted document sent in an email system.

5. See object, object-oriented programming.