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, screenname (or screen name), nickname (or nick) and handle, which is derived from the identical Citizen's Band radio term.
Some software products provide services to other systems and have no direct end users.
End users are the ultimate human users (also referred to as operators) of a software product. The term is used to abstract and distinguish those who only use the software from the developers of the system, who enhance the software for end users. In user-centered design, it also distinguishes the software operator from the client who pays for its development and other stakeholders who may not directly use the software, but help establish its requirements. This abstraction is primarily useful in designing the user interface, and refers to a relevant subset of characteristics that most expected users would have in common.
In user-centered design, personas are created to represent the types of users. It is sometimes specified for each persona which types of user interfaces it is comfortable with (due to previous experience or the interface's inherent simplicity), and what technical expertise and degree of knowledge it has in specific fields or disciplines. When few constraints are imposed on the end-user category, especially when designing programs for use by the general public, it is common practice to expect minimal technical expertise or previous training in end users.
The end-user development discipline blurs the typical distinction between users and developers. It designates activities or techniques in which people who are not professional developers create automated behavior and complex data objects without significant knowledge of a programming language.
A user's account allows a user to authenticate to a system and potentially to receive authorization to access resources provided by or connected to that system; however, authentication does not imply authorization. To log into an account, a user is typically required to authenticate oneself with a password or other credentials for the purposes of accounting, security, logging, and resource management.
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, through a process known as identity correlation. In Unix systems, the username is correlated with a user identifier or user id.
Computer systems operate in one of two types based on what kind of users they have:
Each user account on a multi-user system typically has a home directory, in which to store files pertaining exclusively to that user's activities, which is protected from access by other users (though a system administrator may have access). User accounts often contain a public user profile, which contains basic information provided by the account's owner. The files stored in the home directory (and all other directories in the system) have file system permissions which are inspected by the operating system to determine which users are granted access to read or execute a file, or to store a new file in that directory.
While systems expect most user accounts to be used by only a single person, many systems have a special account intended to allow anyone to use the system, such as the username "anonymous" for anonymous FTP and the username "guest" for a guest account.
Various computer operating-systems and applications expect/enforce different rules for the format.
Some online communities, such as Kik Usernames, use usernames as nickname for the account holders. In some cases, a user may be better known by their username than by their real name, such as CmdrTaco (Rob Malda), founder of the website Slashdot
Some usability professionals have expressed their dislike of the term "user" and have proposed changing it. Don Norman stated that "One of the horrible words we use is 'users'. I am on a crusade to get rid of the word 'users'. I would prefer to call them 'people'."
The down-level logon name format is used to specify a domain and a user account in that domain [...].