A prophet, simply put, is a "speaker" for God (Jeremiah 1:9).
He proclaims a message given to him by God and not from his own spirit (Hebrews 1:1).
A prophet is primarily a preacher of righteousness (Acts 15:32) but sometimes foretell the future (Acts 11:28; Acts 21:10).
He sees and hears things beyond the natural realm usually through visions, dreams, trance, inward voice and unusual visitation of the presence and power of God (Numbers 12:6, Amos 3:7).
He speaks in God's name with God's authority (2Peter 1:20-21)