In
Rabbinic
Judaism,
bechorim, or first born children- male children that is (
of course)- have to fast on the day preceeding the first night of
Passover. This is in commemoration of the
Slaying of the First Born, when
God killed all the first born children and animals in
Egypt and freed the Jewish
slaves. Only the Jewish first born survived, and they are supposed to
fast in
gratitude.
Traditionally, though, this fast is typically circumvented by a
Seudat Mitzvah- literally "commanded meal"- in the form of a
siyyum, or celebration for the completion of some portion of learning.