mahāyoga (Sanskrit). The fourth level of tantric teachings according to the Nyingma school, equivalent in some respects to the Father Tantra class of the New Schools. Many of the tantric texts that form this category are considered to be canonical and thus are included in the Kanjur, although they may be alternative translations.

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