1) A section of a network that is bounded by bridges, routers, or switches. 2) In a LAN that uses a bus topology, a segment is a continuous electrical circuit that is often connected to other such segments with repeaters. 3) A term used in the TCP specification to describe a single transport layer unit of information. The terms datagram, frame, message, and packet are also used to describe logical information groupings at various layers of the OSI reference model and in various technology circles.