It is called the sacrament of Penance, the sacrament of Reconciliation, the sacrament of Forgiveness, the sacrament of Confession, and the sacrament of Conversion.
Since the new life of grace received in Baptism does not abolish the weakness of human nature nor the inclination to sin (that is, concupiscence), Christ instituted this sacrament for the conversion of the baptized who have been separated from him by sin.
The risen Lord instituted this sacrament on the evening of Easter when he showed himself to his apostles and said to them, “Receive the Holy Spirit. If you forgive the sins of any, they are forgiven; if you retain the sins of any, they are retained.” (John 20:22-23).
It is the movement of a “contrite heart” (Psalm 51:19) drawn by divine grace to respond to the merciful love of God. This entails sorrow for and abhorrence of sins committed, a firm purpose not to sin again in the future and trust in the help of God. It is nourished by hope in divine mercy. (Compendium of the Catechism of the Catholic Church, 296-298,300) See more.