Tapas HINDUISM

Tapas, (Sanskrit: “heat,” or “ardour”), in Hinduism, ascetic practice voluntarily carried out to achieve spiritual power or purification. In the Vedas, tapas refers to the “inner heat” created by the practice of physical austerities and figured in the creation myths, as a means by which Prajāpati (the main creator god) brought the world into existence. In later Hinduism the practice of tapas was especially associated with yogic discipline as a way of purifying the body in preparation for the more exacting spiritual exercises leading to liberation (moksha). Among the austerities mentioned in the sacred literature are fasting, the holding of difficult and often painful bodily postures, vigils kept in the presence of fires or extreme cold, and breath control.

In the Jaina religion asceticism is seen as a way of preventing new karma (effect of good or bad action) from forming, as well as a way of getting rid of the old, and is thus one of the central means of breaking the cycle of rebirths. The Jainas distinguish between external tapas, such as fasting (including the most severe form, fasting unto death), restricting the intake of food, meditating, and living in seclusion, and internal tapas, such as contemplation, confession, and repentance of sins.

In early Buddhism the monastic life of chastity and poverty was regarded as the only path to enlightenment. Yet the Buddha renounced the extremes of self-mortification as strongly as he did self-indulgence, in his advocation of the “middle way."

https://www.britannica.com/topic/tapas