Tapas, a central term in Hindu mythology, literally means “heat.” It served as a metaphor for the heat generated in ascetic and esoteric practices. Austerities that generated tapas, often themselves called tapas, were not always ascetic in spirit.
Most myths link tapas with powers (siddhis): one practiced tapas in order to gain siddhis. The demons (asuras) often quit any aspect of their practice that was ascetic (fasting, yoga, meditation, worship) as soon as they acquired the siddhi they sought (immortality, invincibility, and the like).
Often Brahmâ, and sometimes Indra or other devas, granted a boon (vara) for a particular power (siddhi) as a reward for a particular form of austerity (tapas). In this latter conception tapas was analogous to Vedic sacrifice, providing the devas with something they wanted so that they would grant a human desire.
Besides siddhis, these desires could even include the reward of heaven (svarga). Myths about the way the asuras would practice tapas that flattered Brahmâ suggested that repeating a chant (mantra) of praise (japa) for a thousand years either pleased Brahmâ or obligated him to grant the desired boon.
When tapas was equated with purification rituals, it was linked to the notion of penance. However, stories of people becoming purified by penance in order to have the siddhi to make war with invincibility only emphasize the connection of tapas to magic (mâyâ).