In summary: A prophet is a teacher of known truth; a seer is a perceiver of hidden truth, a revelator is a bearer of new truth. In the widest sense, the one most commonly used, the title 'prophet' includes the other titles and makes of the prophet, a teacher, perceiver, and bearer of truth.
What is a prophet of God called?
A prophet is a man called by God to be His representative on earth. When a prophet speaks for God, it is as if God were speaking (see D&C 1:38). A prophet is also a special witness for Christ, testifying of His divinity and teaching His gospel. A prophet teaches truth and interprets the word of God.