A segment is a defined portion or section of something larger such as a database, geometric object, or network. The term is used in database management, graphics, and communications.
1) In a database, a segment is a portion of the database that consists of one or more extents. Each extent is in turn made up of units called blocks, which are the smallest database units. One or more segments make up a tablespace.
2) In graphics, a segment is defined by the shortest possible path between two points. In a bitmap, the thinnest possible segment is the set of all pixels that lie closest to the shortest path between two points. In vector graphics, a segment is generated by specifying two end points and then executing operations that construct a straight line between and including those points. Two or more segments placed end-to-end form a polyline.
3) In communications, a segment is a portion of a network. Within a network segment, data can flow between any two points without having to pass through switches, routers, bridges, or hubs. The size of a segment can be defined by the number of workstations within it, or by the amount of network traffic it carries.