Although the words disciple and apostle are sometimes used interchangeably, they mean different things. A disciple is a follower or student of someone. An apostle is someone who is sent out with a message or mission.
In the Bible, Jesus' disciples were the group of followers who listened and learned from him. The Bible mentions different groups of disciples, including the group of 70 Jesus addressed in the gospel of Luke. Twelve of his disciples became his apostles when they were sent out on a mission to spread "the good news of Christ." Only two of the canonical gospels of the Bible use the word apostles to describe the 12. The other two only refer to them as disciples.
The word Greek word "mathetes," from which the word "disciple" is translated, means "student" or "one who is taught."
Many Jewish and Greek teachers, most notably Socrates and Gamaliel, who was Paul's mentor, had many disciples. The word "apostle" comes from the word "apostolos," which means "messenger." The form of the word that is used in the Bible was rarely in use prior to the New Testament.