In the broadest sense, church discipline is everything the church does to help its members pursue holiness and fight sin. Preaching, teaching, prayer, corporate worship, accountability relationships, and godly oversight by pastors and elders are all forms of discipline.
In a narrower sense, church discipline is the act of correcting sin in the life of the body, including the possible final step of excluding a professing Christian from membership in the church and participation in the Lord’s Supper because of serious unrepentant sin (see Matt. 18:15-20, 1 Cor. 5:1-13).