In the Bible "the Exodus" is the departure of the Israelites out of Egypt under the leadership of Moses, recorded in the book of Exodus, chapters 12-15.
Exodus 12:51 in the King James Version reads:
And it came to pass the selfsame day, that the LORD did bring the children of Israel out of the land of Egypt by their armies.
The verse closes Exodus 12, at the end of the chapter that recounts the first Passover and the departure from Egypt. Read it in context at Exodus 12:51, or the full chapter at Exodus 12. Encyclopedia entry: en.wikipedia.org/wiki/The_Exodus.