A security mechanism in the form of an authentication tool used to identify a user of a device, program, or network and to identify the user's level of privilege on a site, host, application, screen, and field level.A password usually comprises a string of characters that the user enters through a keypad, ideally a reasonably lengthy combination of letters, numbers, punctuation marks, and other characters that an intruder cannot easily guess. Passwords should be changed frequently.A password usually is associated with a user ID, or username, and both must be entered during the logon process. See also authentication and security.