Loving kindness. Mettā or maitrī is benevolence, friendliness, amity, friendship, good will, kindness, close mental union (on same mental wavelength), and active interest in others. It is one of the ten pāramīs of the Theravāda school of Buddhism, and the first of the four sublime states (Brahmavihāras). This is love without clinging (upādāna).
The cultivation of benevolence (mettā bhāvanā) is a popular form of meditation in Buddhism. In the Theravadin Buddhist tradition, this practice begins with the meditator cultivating benevolence towards themselves, then one's loved ones, friends, teachers, strangers, enemies, and finally towards all sentient beings. In the Tibetan Buddhist tradition, this practice is associated with tonglen (cf.), whereby one breathes out ("sends") happiness and breathes in ("receives") suffering. Tibetan Buddhists also practice contemplation of the Brahmavihāras, also called the four immeasurables, which is sometimes called 'compassion meditation'.
"Compassion meditation" is a modern scientific field that demonstrates the efficacy of metta and related meditative practices.
Example video: Sharon discusses the Buddhist concept of Metta or Loving Kindness.
Example via www.ramdass.org: Featured Teacher: Sharon Salzberg
Example via www.mindpodnetwork.com: Metta Hour with Sharon Salzberg