The three outer or lower classes of tantra (Tib. རྒྱུད་སྡེ་འོག་མ་སུམ, ཕྱིའི་རྒྱུད་, gyüdé ok ma sum, chi gyü, Wyl. rgyud sde 'og ma sum, phyi'i rgyud) are classes of tantra which are common to both the Nyingma and Sarma schools of Tibetan Buddhism. They are also called the three tantras of vedic asceticism. They are: