groups(1)
NAME
groups − show group memberships
SYNTAX
groups [user]
DESCRIPTION
The groups command shows the groups to which you or the optionally specified user belong. Each user belongs to a group specified in the password file /etc/passwd and possibly to other groups as specified in the file /etc/group. If you do not own a file but belong to the group which it is owned by then you are granted group access to the file.
When a new file is created it is given the group of the containing directory.
FILES
/etc/passwd, /etc/group