The Book of Exodus gives several descriptions of the food provided by God for the Jews as they meandered through the dessert. Manna is described as fine,white flakes that melt in the sun, and taste like wafers made with honey. Like all fresh food, manna came with a "best used by..." date, which in this case was "best used by tomorrow". If collected and stored, manna became infested with worms and rotted (yech!).
Regardless of what it was, manna was not a food of choice. Back in Egypt, the Children of Israel would not had subsisted on bug poo or lichens. But as they were obviously suffering from problems of food security, God provided the Israelites with daily rations of manna. The manna provided basic subsistence, but not much variety. Manna could be compared to corn meal provided by the USA to Africa - its not the food that they'd choose, but given the alternatives, it did provide nutrition!