The sacrament by which a penitent expressing true contrition, confession, and willingness to make satisfaction through the absolution of a priest reconciles the faithful penitent to God and thereby remits all of his sins.
Catholics in informal conversation nearly always refer to it as Confession. Pope John Paul II called it the Sacrament of Penance because its deepest purpose is penance. CCC 1430, 1431 Penance is a radical reorientation of our whole life, a conversion to God with all our heart. Some Catholics call it the Sacrament of Reconciliation because through it we become reconciled with God.
The matter of this sacrament is the penitent’s contrition, confession, and willingness to make satisfaction.
The form of this sacrament is the priest’s prayer of absolution: “God the Father of mercies, through the death and resurrection of his Son has reconciled the world to himself and sent the Holy Spirit among us for the forgiveness of sins; through the ministry of the Church may God give you pardon and peace, and I absolve you from your sins in the name of the Father, and of the Son, and of the Holy Spirit.”
Penance is a sacrament of the dead, because it confers sanctifying grace even when we are in a state of mortal sin.
Penance is one of the two sacraments of healing. The other is the Sacrament of Anointing of the Sick and Dying.