three vows (Tibetan, sdom-gsum). A Tibetan term for the three levels of moral restraints and ethics, comprising the Vinaya code of discipline, the Bodhisattva vows, and the tantric commitments (samaya). The precise relationship and hierarchy of these three kinds of vows, apparently contradictory in certain respects, gave rise to much debate in Tibetan religious circles.

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