Metta (Pali) is a benevolence toward all beings, without discrimination, that is free of selfish attachment. It is a strong, sincere wish for the happiness of all beings. The Metta Sutta compares metta to the love of a mother, who would give her life for her children.
Metta is often translated as "compassion," which is not inaccurate. However, Pali makes a distinction between metta and karuna, which also means "compassion." Karuna refers to active sympathy and gentle affection, a willingness to bear the pain of others, and possibly pity.