In Pali, the language of the Buddhist script­ures, these four are known under the name of Brahma­-vi­hara. This term may be rendered by: excellent, lofty or sublime states of mind; or altern­ati­vely, by: Brahma­-like, god-like or divine abodes. Four sublime states of mind have been taught by the Buddha:
Love or Loving­-ki­ndness (metta)
Compassion (karuna)
Sympathetic Joy (mudita)
Equanimity (upekkha)

They are said to be excellent or sublime because they are the right or ideal way of conduct towards living beings (sattesu samma patipa­tti). They provide, in fact, the answer to all situations arising from social contact. They are the great removers of tension, the great peace-­makers in social conflict, and the great healers of wounds suffered in the struggle of existence. They level social barriers, build harmonious commun­ities, awaken slumbering magnan­imity long forgotten, revive joy and hope long abandoned, and promote human brothe­rhood against the forces of egotism.

I. Here, monks, a disciple dwells pervading one direction with his heart filled with loving­-ki­ndness, likewise the second, the third, and the fourth direction; so above, below and around; he dwells pervading the entire world everywhere and equally with his heart filled with loving­-ki­ndness, abundant, grown great, measur­eless, free from enmity and free from distress.

II. Here, monks, a disciple dwells pervading one direction with his heart filled with compas­sion, likewise the second, the third and the fourth direction; so above, below and around; he dwells pervading the entire world everywhere and equally with his heart filled with compas­sion, abundant, grown great, measur­eless, free from enmity and free from distress.

III. Here, monks, a disciple dwells pervading one direction with his heart filled with sympat­hetic joy, likewise the second, the third and the fourth direction; so above, below and around; he dwells pervading the entire world everywhere and equally with his heart filled with sympat­hetic joy, abundant, grown great, measur­eless, free from enmity and free from distress.

IV. Here, monks, a disciple dwells pervading one direction with his heart filled with equani­mity, likewise the second, the third and the fourth direction; so above, below and around; he dwells pervading the entire world everywhere and equally with his heart filled with equani­mity, abundant, grown great, measur­eless, free from enmity and free from distress.

Mettā (Skt. maitri­)—l­oving kindness, benevo­lence, goodwi­ll—is defined as that which softens one’s heart. It is not carnal love or personal affection. The direct enemy of mettā is hatred, ill will or aversion (kodha), its indirect enemy is personal affection (pema).

Mettā embraces all beings without exception. The culmin­ation of mettā is the identi­fic­ation of oneself with all beings (sabba­ttatā) . It is the wish for the good and happiness of all. Benevolent attitude is its chief charac­ter­istic. It discards ill will.

Karuņā (compa­ssion) is defined as that which makes the hearts of the good quiver when others are subject to suffering, or that which dissipates the sufferings of others. Its chief charac­ter­istic is the wish to remove the sufferings of others. Its direct enemy is wickedness (hiṃsā) and its indirect enemy is passionate grief (doman­assa). Compassion embraces sorrow­-st­ricken beings and it eliminates cruelty.

Muditā is not mere sympathy but sympat­hetic or apprec­iative joy. Its direct enemy is jealousy (issā) and its indirect enemy is exhila­ration (pahāsa). Its chief charac­ter­istic is happy acquie­scence in others’ prosperity and success (anumo­danā). Muditā embraces all prosperous beings. It eliminates dislike (arati) and is the congra­tul­atory attitude of a person.

Upekkhā literally means to view impart­ially, that is, with neither attachment nor aversion. It is not hedonic indiff­erence but perfect equanimity or well-b­alanced mind. It is the balanced state of mind amidst all viciss­itudes of life, such as praise and blame, pain and happiness, gain and loss, repute and disrepute. Its direct enemy is attachment (tāga) and its indirect enemy is callou­sness. Upekkhā discards clinging and aversion. Impartial attitude is its chief charac­ter­istic. Here upekkhā does not mean mere neutral feeling, but implies a sterling virtue. Equani­mity, mental equili­brium are its closest equiva­lents. Upekkhā embraces the good and the bad, the loved and the unloved, the pleasant and the unpleasant