terma (Tibetan, gter-ma). Literally ‘hidden treasure’, termas are believed to be texts hidden in Tibet during the First Propagation period by Padmasambhava and others to be later discovered and disseminated by ‘treasure revealers’. These texts are venerated as authentic revelations of the Dharma by adherents of the Nyingma school and include such works as the ‘Tibetan Book of the Dead’ ( Bar-do thos-grol). There are Indian antecedents for this belief in hidden literary treasures as many Mahāyāna scriptures are said to have come to light in India in a similar manner.

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