What is Monosaccharide?

A Monosaccharide is just the simplest form of sugar. It's general term applied to a sugar that cannot be broken down into anything 'simpler'. A great example of this is glucose. Glucose cannot be hydrolized to form anything else, but there are more complex forms of glucose like glycogen. Glycogen is basically a bunch of glucose molecules bonded together and used as "stored glucose", but glycogen can be hydrolized to form individual glucose molecules (monosaccharides).