Counselor
Counselor is an official post on large Federation starships in the 24th century.
Nature of the Post
Deanna Troi held the post of Counselor on the Enterprise-D. Her primary duty was apparently to advise the Captain on matters of crew morale and use her psychology skills to assist in any negotiations that occurred. As a half-Betazoid, her empathic abilities gave her an advantage in such negotiations, but not all Starfleet Counselors have telepathic abilities.
Criticism
Why Starfleet made a Counselor a bridge crew member on Federation starships is something of a mystery; Counselor Troi started the job without qualifications for any bridge position (navigation, ops, tactical, etc.); her training in psychology was her only job skill. Critics of TNG have occasionally wondered if the Counselor on a Federation starship is a kind of "political officer" tasked with monitoring the activities of the command staff and reporting them back to Starfleet headquarters.