1. Originally, a clearly identifiable set of data, or code, that was moved between backing store and main memory under the control of the user. Later the term was applied to a set of data, still clearly visible to the user, that was managed by the operating system as part of the virtual memory system. A segment differs from a page in that its size is not fixed, and the user has a measure of direct control over its management.

2. Part of a program. The word is usually used in the context of storage allocation, as in code segment, data segment.

3. A region of near-uniform intensity in a grey-level image that represents a distinct entity. Segmentation is the image processing stage that locates and divides up an image into segments.

4. of an Ethernet. A part of an Ethernet that consists of a single length of cable, usually coaxial cable. There are strict limits on the total length of cable that can be used. See also Ethernet, thick wire.