In Jainism, Athai Tap (also called Ashtahnika Tap) refers to a specific type of austerity or penance where a person eats only once a day (ekasana) for eight consecutive days. This vow is considered highly meritorious and is typically observed with great devotion, often during the Ashtahnika Parva, which comes three times a year in the Jain calendar.

So yes, if you observe ekasana (eating only once a day) for eight continuous days, it is called Athai Tap. This penance is done with the intention of self-purification, accruing punya (spiritual merit), and progressing on the path of liberation. The practice should be undertaken with proper niyama (vows and discipline), and ideally under the guidance of a knowledgeable Jain teacher or monk.