On the day before Passover, the first-born of our people fast to commemorate their being spared the fate of the first-born Egyptians. But one may eat if he is participating in a Seudat Mitzvah, the festive repast which accompanies the performance of certain mitzvot.
One such mitzvah is Talmud Torah study. Thus, when a scholar completes a significant section of material (e.g., a tractate of Talmud), it is customary for all present to join in a siyyum, a ceremony of completion with a meal. Any first-born who participates in the ceremony may eat. This is known as the Siyyum B'chorim. Beginning at about 8:15 a.m., the Siyyum will be held after the 7:30 morning minyan.