The Tapa (austerity or penance) performed in lieu of Prāyaścita (expiation) for purification of trangression committed with respect to the Mulaguṇa (principal virtue) or the Uttaraguṇa (secondary virtue). The duration of such Tapa is fasting for five day-nights in minimum and for six months in maximum.
tavo mūhittaraguṇātiyāre paṃcarātimdiyāti chammāsāvasāṇamaṇekadhā.
(ĀvaCū 2 p. 246)