A siyum celebration often lets firstborn Jews break the Fast of the Firstborn before Passover.
A siyum marks the completion of a substantial unit of Jewish learning, commonly a tractate of the Talmud. It is usually followed by a seudat mitzvah, a celebratory meal connected with a religious commandment. Attending that meal gives the firstborn a customary way to end the fast.
The Fast of the Firstborn, or Ta'anit Bekhorot, is generally observed on 14 Nisan, the day before Passover. It commemorates the Israelite firstborns being spared during the final plague in Egypt. In modern practice, many synagogues schedule a siyum after morning prayers so participants can eat rather than continue fasting.
A siyum is not the same as an ordinary social gathering or Kiddush. The learning must genuinely reach a completion, and authorities discuss whether participants must hear the conclusion and eat at the associated meal. Practices also vary among communities, and some firstborns continue to fast or follow other customs.