1. An individual process in a group of processes, a portion of an overall job. Software projects are often broken down into phases. 2. In electricity, the type of electrical service, most often single phase for residential use or three phase for industrial use. In the case of single phase, it is relating to a circuit energized by a single alternating electromotive force; in three phase, it is relating to, or operating by means of a combination of three circuits energized by alternating electromotive forces (EMF) that differ in shift phase by one third of a cycle.