Where did the phrase “manna from heaven” come from and What does it mean?

The phrase “manna from heaven” means a windfall; something providential.

That is the current figurative use of the expression; but, as any biblical student knows, the real manna from heaven was that spoken of in the sixteenth chapter of Exodus, “a small round thing, as small as the hoar frost on the ground,” which provided the needed food for the children of Israel on their journey out of Egypt.