Questions related to פֶּסַח "pesach" -- the festival associated with the exodus from Egypt.
The "Passover" was instituted in the book of Exodus (see Exod. 12:23 and 34:25), and became part of the annual holy days of Judaism. It also features in a significant way in the story of the New Testament, as the events of the passion narrative are set during this festival.
For further information on the festival, its origins, and later development, see the relevant sections of the "Passover" articles in the Encyclopedia Judaica (2008),
1 and the Jewish Encyclopedia (1906).
1 The EJ link points to a version in the Archive.org Wayback Machine, as the current article on the Jewish Virtual Library site has been abbreviated.