Users
Users in a computing context refers to one who uses a computer system. Users may need to identify themselves for the purposes of accounting, security, logging and resource management. In order to identify oneself, a user has an account (a user account) and a username , and in most cases also a password (see below). Users employ the user interface to access systems.
Users are also widely characterized as the class of people that uses a system without complete technical expertise required to fully understand the system. In most hacker-related contexts, they are also called lusers or power users. See also End-user (computer science).
Screen names (also called a handle, nickname, or nick on some systems) refer to a public name that can be used to ’screen’ ones true user name from the public eye. Services such as AOL allowed customers to have multiple screen names per user name, and IRC nicks are independent of one’s system account username.
For instance, one can be a user of (and have an account on) a computer system, a computer network and have an e-mail account, an IM account and use one or more nicks on IRC.
In wikipedia(http://en.wikipedia.org/wiki/User_%28computing%29
