from
The Free On-line Dictionary of Computing (8 July 2008)
user name
<operating system, security> (Or "logon") A unique name for
each user of computer services which can be accessed by
several persons.
Users need to identify themselves for accounting, {security},
logging, and {resource management}. Usually a person must
also enter a {password} in order to access a service. Once
the user has logged on the {operating system} will often use a
(short) {user identifier}, e.g. an integer, to refer to them
rather than their user name.
User names can usually be any short string of alphanumeric
characters. Common choices are first name, initials, or some
combination of first name, last name, initials and an
arbitrary number. User names are often assigned by {system
administrators} according to some local policy, or they may be
chosen by the users themselves.
User names are often also used as {mailbox} names in
{electronic mail} addresses.
(1997-03-16)