Fast of the Firstborn.
It is a widespread custom that the first born fast on the day before Pesah. This commemorates the divine protection of the Israelite firstborn during the final plague in Egypt. However, it is also prohibited to fast during the month of Nisan. There is a standard solution to this paradox: a siyyum, a public completion of study of a tractate of the Talmud. After this, first born participants may eat a meal in celebration of the event, and having eaten, a first born need not fast the remainder of day. (The Rabbinical Assembly)
