Austerties (or penance)- That which heats up (burns up) and destroys the eight types of Karmic knots or Kārmaṇaśarīra (subtlemostbody formed by Kama-pudgalas (material clusters qua Karma)). It is the cause of annihilation of the previously bound Karma.
tavo ṇāma tāvayati aṭṭhavihaṃ kammagaṃṭhiṃ nāseti ttivuttaṃ bhavai.
(Da 8.62 JiCū p.15)
purvagṛhītakarmakṣayahetuśca tapaḥ.
(ONiVṛ Pa 12)