Ta’anit Bechorot (or Ta’anit Bekhorot – “Fast of the First Born”) is a fast day from sunrise until sunset on the day before Passover, the first born male of every Jewish household fasts in commemoration of the 10th plague of Passover, in which HaShem spared the first born male in every Jewish household in Egypt, and instead slew the first born in every Egyptian household.
There are several traditions concerning the fast day and how rigidly it is observed. If there is no first born male in a Jewish household, then the oldest male in the family fasts. If there are no children, then the oldest member of the family fasts, usually the father of the household. This is done because all Egyptian families were affected by HaShem’s wrath, whether or not they had a first born son.
First borns can be exempted from the Ta’anit Bechorot by attending a Siyyum Bekhorot. Siyyum means “the celebration held after the public completion of study of a tractate of the Talmud or at the end of a year of study” in Hebrew, and Siyyum Bekhorot means “the celebration held after the public completion of study of a tractate of the Talmud or at the end of a year of study for first borns”. This celebration usually involves eating at a feast. The Siyyum Bekhorot is done so that the obligation or mitzvah to hold a celebration will override the mitzvah to fast on the day before Passover.