On UNIX based systems, groups and users can have the same name. For the GRANT statement, you must specify whether you are referring to a group or to a user. For the REVOKE statement, specifying user or group depends on whether or not there are multiple rows in the authorization catalog tables for the GRANTEE with different values of GRANTEETYPE.
On OS/2, groups and users cannot have the same name.
On Windows NT, Local Group names, Global Group names, and User IDs cannot have the same name.
Group names cannot exceed 8 characters.