The word, Christian, comes from the Greek word, christianos, which is derived from the word, christos or Christ, which means "anointed one." A Christian, then, is someone who is a follower of Christ. The first use of the word, "Christian," in the Bible is found in Acts 11:26, "And the disciples were called Christians first in Antioch." It is found only twice more in Acts 26:28 and 1 Pet. 4:16. However, it is important to note that it is the true Christ that makes someone a Christian and not the Mormon one (brother of the devil, see Mormon Beliefs for more information) or the Jehovah's Witnesses' one (Michael the Archangel), the New Age Jesus (a man in tune with the divine Christ Consciousness), etc. The true Christ is God in flesh (John 1:1, 14, 20:28, Col. 2:9, Phil. 2:5-8, Heb. 1:8): Jesus.
Christianity teaches the following: there is only one God in all existence, God is a Trinity, Jesus Christ is God in flesh, salvation is by grace alone through faith alone, Jesus died on the cross, and Jesus rose from the dead in a glorified, physical body. The religion that contradicts any of these teachings is not Christian.
See the Christian Doctrine Grid