What does "seder" mean?
The Hebrew word seder means “order” and refers to the religious service and festive meal observed in Jewish households on Pesach. Seder derives from the same root as the Hebrew word siddur (prayer book). Just as the siddur contains the order of prayers for daily, Shabbat, and festival services, so is the seder a prescribed order of prayers, readings, symbolic explanations, and songs related to Pesach. The Pesach seder is the only ritual meal in the Jewish calendar year for which such an order is prescribed, hence its name.