triyāna (Skt, three vehicles). In Mahāyāna literature, a name used for the three ways to salvation. These are: (1) the Śrāvakayāna or ‘vehicle of the hearers’ (also known as the Hīnayāna); (2) the Pratyekabuddhayāna or ‘vehicle of the Solitary Buddhas’; and (3) the Bodhisattvayāna or ‘vehicle of the Bodhisattvas’. Different ‘vehicles’ are said to have been taught by the Buddhas at different times as appropriate for different individuals. According to the Mahāyāna, however, the highest and greatest is the last.

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

theg pa gsum

[translation-san] {L,MSA} triyāna

[translation-san] {MSA,MV} yāna-traya

[translation-eng] {Hopkins} three vehicles

[division-bod] theg dman/ rang rgyal gyi theg pa/ theg chen/

[division-eng] Div.: (1) Hearer Vehicle (śrāvaka-yāna); (2) Solitary Realizer Vehicle (pratyekabuddha-yāna); and (3) Bodhisattva Vehicle (bodhisattva-yāna)

Jeffrey Hopkins' Tibetan-Sanskrit-English Dictionary