Catholics believe that the sacraments are an outward sign of an inward grace. In this case, the outward sign is the absolution, or forgiveness of sins, that the priest grants to the penitent (the person confessing his sins); the inward grace is the reconciliation of the penitent to God. That is why the Sacrament of Confession is sometimes called the Sacrament of Reconciliation. Whereas Confession stresses the action of the believer in the sacrament, Reconciliation stresses the action of God, who uses the sacrament to reconcile us to Himself by restoring sanctifying grace in our souls.
The CCC (Catechism of the Catholic Church) refers to the Sacrament of Confession as the Sacrament of Penance. Penance expresses the proper attitude with which we should approach the sacrament, with sorrow for our sins, a desire to atone for them, and a firm resolve not to commit them again. Confession is less frequently called the Sacrament of Conversion and the Sacrament of Forgiveness.