Manna has a Greek root that comes from the Hebrew man, and although it literally means "substance exuded by the tamarisk tree," it's almost always used to refer to God's nourishment in the Bible. You might, for example, say, "The doughnuts my coworker brought in this morning were like manna from heaven."
When Jesus initially claimed that He is the Bread of Life, and that eternal life was offered only to those who believe in Him, the people were indignant. They demanded that Jesus perform a miracle to prove Himself, despite having just witnessed His miracles of healing and provision (John 6:2; John 6:9–14; John 6:30–31). They also invoked the miracle of manna which was given to Israel in the wilderness (Exodus 16), almost daring Jesus to do something more spectacular than that.
The favored theory on what the Israelites called manna is the sap of a tamarisk tree. In Calabria and Sicily, Italian farmers cut the bark of the flowering ash (Fraxinus ornus) to get the dried sap, the only domesticated form of manna. Known as 'Nectar of the Gods', the Sicilian Manna is a typical local product of the Italian island, with a characteristic sweet taste.