(Luke 6:12-16)
Although Jesus had many disciples (learners, or followers), He chose 12 apostles. The word apostle means "one who is sent out with a special message." These men were His inner circle, to whom He gave special training before sending them out with His authority.

Except for Judas Iscariot, the traitor, these were the men who started the Christian church. In the Gospels, these 12 men are usually referred to as the disciples. In the book of Acts, in the New Testament, they are called apostles.
(Life Application Bible, New International Version, Tyndale House Publishers, Inc., Wheaton Illinois, and Zondervan Publishing House, Grand Rapids, Michigan, 1991, 1806.)