Mettā (Pali) means benevolence, loving-kindness, friendliness, amity, friendship,good will, kindness, and active interest in others.
It is the first of the four sublime states (Brahmavihāras) and one of the ten pāramīs of the Theravāda school of Buddhism.
The cultivation of benevolence is a popular form of meditation in Buddhism in the Theravadin Buddhist tradition. In the Tibetan Buddhist tradition, it is part of the Brahmavihara meditation (four immeasurables). Metta as compassion meditation is often practiced in Asia by broadcast chanting, wherein monks chant for the laity.
The compassion and universal loving-kindness concept of Metta is discussed in the Metta Sutta of Buddhism, and is also found in the ancient and medieval texts of Hinduism and Jainism as Metta or Maitri.
Small sample studies on the potential of loving-kindness meditation approach on patients suggest potential benefits. However, peer reviews question the quality and sample size of these studies, then suggest caution.
Karuṇā is important in all schools of Buddhism.
For Theravāda Buddhists, dwelling in karuṇā is a means for attaining a happy present life and heavenly rebirth.
For Mahāyāna Buddhists, karuṇā is a co-requisite for becoming a Bodhisattva.
Upekkhā (Pali), is the Buddhist concept of equanimity.
As one of the Brahma Vihara (meditative states), it is a pure mental state cultivated on the Buddhist path to nirvāna.
Muditā (Pāli) means joy; especially sympathetic or vicarious joy.
Also: the pleasure that comes from delighting in other people's well-being.
The traditional paradigmatic example of this mind-state is the attitude of a parent observing a growing child's accomplishments and successes. Mudita should not be confounded with pride as a person feeling mudita may not have any interest or direct income from the accomplishments of the other. Mudita is a pure joy unadulterated by self-interest.
When we can be happy of the joys other beings feel, it is called mudita; the opposite word is envy or schadenfreude.