In the Bible, Passover marks the Exodus of the Children of Israel from Egyptian slavery, when God “passed over” the houses of the Israelites during the last of the ten plagues. When the Temple in Jerusalem stood, the paschal lamb was offered and eaten on Passover eve, while the wave offering of barley was offered on the second day of the festival. Nowadays, in addition to the biblical prohibition of owning leavened foods for the duration of the holiday, the Passover seder is one of the most widely observed rituals in Judaism.
https://en.wikipedia.org/wiki/Passover