Passover is the religious festival that celebrates the deliverance of Israel from the bondage of the Egyptians. The term is derived from the Hebrew pasach which means "to pass over."
When the Jews were in slavery to the Egyptians, the Lord raised up Moses to be their deliverer. Moses told the Pharaoh about the plagues that would descend upon the Egyptian people if Pharaoh would not let God's people go. Of course, Pharaoh refused, and the plagues hit Egypt with a fury. The last plague was the death of the first born of each family who lived in Egypt. Since the Jews lived in Egypt, they were subject to this plague the same as the Egyptians. However, the Lord provided a means of protection. If they would take the blood of a lamb and spread it over the doorposts of their homes, the Lord would "pass over" them and the firstborn in their homes would be spared. Exodus 12:13, "And the blood shall be a sign for you on the houses where you live; and when I see the blood I will pass over you, and no plague will befall you to destroy you when I strike the land of Egypt."
It should be obvious that the Passover is typological of Christ. The shed blood of the lamb, of course, represents the shed blood of Christ. The Lord passed over the homes whose doors were covered in blood. That is, the judgment of God was not carried out upon those who were under the blood of the lamb.
After the Lord killed the firstborn in all the households of Egypt, Pharaoh let the Israelites go.