29 At midnight the LORD struck down all the firstborn in the land of Egypt, from the firstborn of Pharaoh who sat on his throne to the firstborn of the captive who was in the dungeon, and all the firstborn of the livestock.
30 And Pharaoh rose up in the night, he and all his servants and all the Egyptians. And there was a great cry in Egypt, for there was not a house where someone was not dead.
31 Then he summoned Moses and Aaron by night and said, "Up, go out from among my people, both you and the people of Israel; and go, serve the LORD, as you have said.
32 Take your flocks and your herds, as you have said, and be gone, and bless me also!"
God fulfilled his promise to Pharaoh by sending this terrible plague, killing all of the first-born in Egypt. This event is known as Passover because God passed over those who listened to his voice and marked their houses with blood from a lamb.
Passover appears again in the New Testament and is a sort of prophecy in itself. This prophecy points to Jesus, the Son of God. Jesus is (at times) called the lamb of God and by his blood, shed on the cross, God passes over our punishment due to us for our sin if we believe in him.