A disciple is one who learns from another, particularly one of the twelve Apostles of Jesus Christ but also referring to those who learn from them, from the Church Fathers, or from any spiritual father.
The term Disciple, which is derived from the Latin discipulus—pupil, from discere, which means to learn, also denotes disciplined learning by a follower. From discipline: training expected to produce a specific character or pattern of behavior, especially training that produces moral or mental improvement, controlled behavior resulting from disciplinary training; self-control.
Original Biblical usage in the Greek New Testament is distinctly different from the Latin understanding. The Greek, μαθητής, (mathetis) originally simply meant a pupil or someone who learns (from matheno). With regards to Jesus' original fellowship, it refers to a close continual teacher/student relationship where learning is greatly emphasised.