(Sanskrit तारा; Tibetan: Dolma) Literally, "savior" or "she who liberates." A symbolic representation of the Divine Mother, who is formless but takes forms like this out of compassion for beings like us.
In Hinduism, Tara is seen as a form of Shakti, the vital energy of the gods, and is thus a manifestation of Durga or Parvati. In Hindu Tantra, Tara is very similar to Kali.
In Tibetan Buddhism, Tara is seen as an emanation of Avalokitesvara (Christ). She is considered the embodiment of the compassion of all the gods, and is thus seen as the mother of all the Buddhas. She appears in twenty-one forms; the two most common are White Tara (associated with healing and long life) and Green Tara (associated with protection). Her veneration is very popular in Tibetan Buddhism.
The mantra of Tara is oṃ tāre tuttāre ture svāhā (oṃ tāre tu tāre ture soha).
For more information, study The Arcanum Twenty-one.