MediaWiki:Userrights-groups-help

You may alter the groups this user is in:
 * A checked box means the user is in that group.
 * An unchecked box means the user is not in that group.
 * A * indicates that you cannot remove the group once you have added it, or vice versa. Note that bureaucrat right cannot be added once they are removed even if there is no * to indicate this.
 * More information on what each group means can be found at Help:User access levels