Sister Concern

What is th definition of sister concern? The term is defined under which act? In case of NPA provisioning, as per RBI norms, when any account is declared NPA; whether 'all facilities are to be regarded as NPA and provision on the same to be made' implies all sister concerns also? If yes, if personal account of individual is NPA, whether partnership account wherein he is only 1% partner is also to be considered NPA?