Excommunication is the act of discipline where the Church breaks fellowship with a member who has refused to repent of sins. Matt. 18:15-18 is generally used as the model of procedures leading up to excommunication. Those excommunicated are not to partake in the Lord’s supper.
In the Bible, serious offenders of God’s law, who were supposed to be Christian, were "delivered over to Satan for the destruction of the flesh," (1 Cor. 5:5, 1 Tim. 1:20). However, upon repentance, the person is welcomed back into fellowship within the body of Christ.