Tārā 

An important female deity in Tibetan Buddhism. Tārā is a Sanskrit word the precise meaning of which is uncertain (perhaps ‘star’), but is understood by Tibetans to mean ‘saviouress’. She is regarded with great affection and devotion by Tibetans, and her cult occupies a status similar to that of the Virgin Mary in Christianity. She is closely associated with Avalokiteśvara (Tibetan, Chenrezi), the Bodhisattva of compassion (karuṇā), of whom she is said to be an emanation. According to one account, she sprang from the tears of Chenrezi as he was about to enter final nirvāṇa. When he looked back and saw the suffering beings who still remained to be saved he wept and decided to remain until all beings had reached salvation. Tārā embodies and expresses the compassionate nature of this Bodhisattva. Many sources regard her as a Buddha and speak of her as the ‘mother of all the Buddhas’. The cult of Tārā became widespread in Tibet with the arrival of Atiśa in 1042, who was a lifelong devotee. In iconography, Tārās of various colours are encountered, the two most common being white and green. The former was the earlier and the latter has a closer association with tantric sources. In all, 21 Tārās are recognized in Tibetan Buddhism. These are referred to in the main liturgical text associated with her cult, Homage to the Twenty-One Tārās, brought from India by Dharmadra in the 11th century. Each Tārā has a different function (curing illnesses, averting disasters, etc.) and each has its own distinct iconographical gestures (mudrās), and sacred syllables (mantras). The main Tibetan schools revere different forms of Tārā, but her mantra om tāre tuttāre ture svāhā (meaning roughly ‘Praise to Tārā, Hail!) is one of the most popular invocations for all Tibetans.

A Dictionary of Buddhism, Oxford University Press, 2003, 2004 (which is available in electronic version from answer.com)

Tārā (f.) [Sk. tārā=Gr. a)sth/r, a)/ston (=Lat. astrum, in E. disaster), Lat. stella, Goth. staírnō, Ohg. sterro (:E. star), perhaps loan word from Semitic sources] a star, a planet Sn 687 (tārāsabha the lord, lit. "the bull" of the stars, i. e. the Moon).
   -- gaṇa (tāra˚) the host of stars Pv ii.967 (cando va t. -- gaṇe atirocati). -- maṇivitāna "star -- jewel -- awning"; canopy of jewelled stars Vism 76.

Pali-English Dictionary, TW Rhys Davids, William Stede,