1. Falling off (wearing off) of Karma (or shedding Karma)- Separation of the Karma-pudgalas (material clusters qua Karma) from the soul, after they themselves have come into the state of fruition or they have been brought to the state of fruition through Udlraṇā (premature rise).
vipakvānāṃ karmāvayavānāṃ pariśaṭanaṃ hānirityarthaḥ. tapasāsevyamānena karmaṇyātmapradeśebhyo vigliaṭanta iti.
(TaBhā 9.3 Vṛ)
2. One of the nine Tattvas (categories of truth);
the purification of the soul attaind on account of the separation of Karmic dirt from it by means of Tapa (austerity or penance).
3. Tapa (austerity or penance) itself is also called Nirjarā by way of transference of epithet.
tapasā karmavicchedādātmanairmalyaṃ nirjarā. upacārāttapo'pi.
(Jaisidī 5.16,17)