from
The Free On-line Dictionary of Computing (8 July 2008)
user identifier
user id
<operating system> 1. (Or "uid", "user id") A number or name
which is unique to a particular user of a computer or group of
computers which share user information. The {operating
system} uses the uid to represent the user in its data
structures, e.g. the owner of a file or process, the person
attempting to access a system resource etc.
A user database, e.g. {Unix}'s /etc/passwd file or {NIS}, maps
the uid to other information about that user such as their
{user name}, {password}, {home directory} and real name.
2. {user name}.
(1997-03-01)