Tapas (tapas) in Sanskrit means "heat". In Vedic religion and Hinduism, it is used figuratively, denoting spiritual suffering, mortification or austerity, and also the spiritual ecstasy of a yogin or tāpasa (a Vriddhi derivative meaning "a practitioner of austerities, an ascetic"). In the Rigveda, the word is connected with the Soma cult. The adjective tapasvin means "wretched, poor, miserable", but also "an ascetic, someone practicing austerities".
In the yogic tradition, tapasyā may be translated as "essential energy", referring to a focused effort leading towards bodily purification and spiritual enlightenment. It is one of the Niyamas (observances of self-control) described in the Yoga Sutras of Patanjali. Tapasya implies a self-discipline or austerity willingly expended both in restraining physical urges and in actively pursuing a higher purpose in life. Through tapas, a yogi or spiritual seeker can "burn off" or prevent accumulation of negative energies, clearing a path toward spiritual evolution.
Personified, Tapasya appears as the father of Manyu in the Rigveda. The tapo-raaja ("king over austerities") is a name of the Moon.
Sanskrit tapasyā (neuter gender), literally "produced by heat", refers to a personal endeavor of discipline, undertaken to achieve a goal, accompanying suffering and pain. Earliest reference of this word is to be found in the Rgveda-7.82.7a, where it is used in the sense 'pain, suffering' (Monier-Williams). It is usually applied in religious and spiritual terms, but can be applied to any field or context. One who undertakes tapas is a Tapasvin. From tapas the more widespread word tapasyā was derived, which is used in all three genders and was mentioned in Katyayana-Shrauta-Sutra, Baudhayana's Dharma-shashtra, Panini-4.4.128, etc. Rigveda has dozens of references to words derived from 'tapas' which indicate that "suffering, austerity" was its meaning from the Rigvedic times.
Monks and gurus in Hinduism, Budhism and Jainism practice tapasya as a means to purify and strengthen their devotion to God, practice a religious lifestyle and obtain moksha, or spiritual liberation.
Tapas may be the striving for nirvana, or moksha. It may also be striving for perfection in a particular sport, field of knowledge or work. Tapasya may also be undertaken as penance, to liberate oneself from the consequences of a sin or sinful activities, or karma. But it will be wrong to equate Tapasya with penance, as done by some scholars. Tapasya can be done for a penance but it is definitely not a penance. Main motive of Tapasya can vary from spiritual gain, penance and even material gain.