In computing, a user is a person who uses a computer or Internet service. A user may have a user account that identifies the user by a username (also user name), screen name (also screenname), or "handle", which is derived from the identical Citizen's Band radio term. To log in to an account, a user is typically required to authenticate himself/herself with a password or other credentials for the purposes of accounting, security, logging, and resource management. For a discussion of user satisfaction, see Computer user satisfaction.
Users are also widely characterized as the class of people that use a system without complete technical expertise required to fully understand the system. In most hacker-related contexts, they are also divided into lusers and power users. Both are terms of opprobriation, but the latter connotes a "know-it-all" attitude. See also End-user (computer science).
A user account allows one to authenticate to system services. It also generally provides one with the opportunity to be authorized to access them. However, authentication does not automatically imply authorization. Once the user has logged on, the operating system will often use an identifier such as an integer to refer to them, rather than their username. On Unix systems this is called the user identifier or user id.
Computer systems are divided into two groups based on what kind of users they have: