Tapas (tapas)

Tapas is heat generated by austerity, the accumulated power of fasting, standing in the sun, holding a posture or keeping a vow for years. In the Mahabharata it is a genuine force with physical effects: gods grow alarmed when a mortal accumulates too much of it, and boons are granted as much to defuse it as to reward it. Arjuna wins the Pashupata by it, Amba builds a whole rebirth on it, and Vishvamitra uses it to force his way from king to brahmin sage.