User

An entity that is interested in interacting with a particular physical entity.

A user is a person who uses a computer or network service. Users generally use a system or a software product without the technical expertise required to fully understand it. Power users use advanced features of programs, though they are not necessarily capable of computer programming and system administration. A user often has a user account and is identified to the system by a username (or user name). Other terms for username include login name, screen name (or screenname), nickname (or nick) and handle, which is derived from the identical Citizen's Band radio term.