Passover is a Jewish festival that commemorates the liberation of the Israelites from Egypt.
When the people of Israel were slaves in Egypt, God sent Moses to free His people. After nine plagues, Pharaoh still did not let the people go so God would now release the tenth and worst plague. It would be the death of every firstborn in Egypt, both animal and person. God told His people to take a bunch of hyssop, dip in the blood of a slaughtered lamb, and mark the lintel and the two doorposts of their homes. At midnight the Lord passed through the land and struck down every firstborn in Egypt but when He saw the blood he passed over that house. That very night Pharaoh summoned Moses and finally freed the people of Israel.