Reparation is the moral obligation to make amends for the harm caused by one's sins. In the context of justice, this means returning stolen goods or compensating someone for physical, financial, or reputational damage (such as slander). Without the sincere intention to make reparation, repentance is incomplete (CCC 2412, 2487).
Spiritual Reparation
On a spiritual level, reparation refers to acts of prayer, penance, and devotion offered to God to repair the damage done to our relationship with Him by our own sins or the sins of others. Through grace, Christians can unite their own acts of spiritual reparation and suffering to the perfect and infinite reparation that Jesus Christ offered to the Father on the Cross (CCC 1459, 2148).
May the Lord bless you and keep you.