[ Thanks to dave for
this link. ]
“Linux users can login to the system and use with the
provided previliges. Linux groups are a mechanism to manage a
collection of computer system users. All Linux users have a user ID
and a group ID and a unique numerical identification number called
a userid (UID) and a groupid (GID) respectively. Groups can be
assigned to logically tie users together for a common security,
privilege and access purpose.”