Fasting for one dayA type of Anaśana (fasting); the Pratyākhyāna (1) (formal resolve (vow) of abstinence)) of (abstinence from) taking food, in which fasting is undertaken from the sunset of the first day up to the sunrise of the third day (in all, missing three meals, taking food on the fourth meal).
caturtham bhaktam yāvadbhaktam tyajyate yatra taccaturtham, iyam copavāsasya samjnā.
(Bhaga 2.62 Vr)
'cautthabhattiyassa'....ekam pūrvadine dve upa-vāsadine caturtham pāranakādine bhaktam bhojanam pariharati yatra tapasi tatcaturtha bhaktam, tad yasayāsti sa caturthabhaktivyah.(Sthā 3.37 Vr Pa 137)
See - Abhaktārtha.