The Trusted user rights group is a user group that grants members the "autopatrol" user right - that is, anyone in the Trusted group will have their edits automatically marked as patrolled and thus bypass the RC and NP patrol queues. Patrollers and administrators may grant/revoke Trusted rights at Special:UserRights. No reason needs to be provided when granting the Trusted group, since the conditions for granting Trusted are clear, though you may wish to provide one if revoking Trusted.