Ta'anit Bechorot for Hebrew Year 5778 occurred on .
Fast of the Firstborn (Hebrew: תענית בכורות, Ta’anit B’khorot or תענית בכורים, Ta’anit B’khorim); is a unique fast day in Judaism which usually falls on the day before Passover. Usually, the fast is broken at a siyum celebration (typically made at the conclusion of the morning services), which, according to prevailing custom, creates an atmosphere of rejoicing that overrides the requirement to continue the fast. Unlike most Jewish fast days, only firstborns are required to fast on the Fast of the Firstborn.
Read more from Judaism 101 →
or Wikipedia →