Forgiveness falls under the virtue category of Temperance. Temperance deals with strengths that protect us from excess. It is the practiced ability to monitor and manage one's emotions, motivation and behavior in the absence of outside help.
It is important to distinguish forgiveness from:
condoning (removes the offense)
forgetting (removes the awareness)
reconciliation (restores the relationship)
Instead forgiveness is a strength that we employ to protect ourselves from the feeling of hatred. It is a specialized form of mercy; a general concept of feeling kindness and compassion towards others.