Explain the term of Monosaccharides?

Monosaccharides :  The simplest carbohydrates are Monosaccharides, simple sugars. These generally have three to six carbon atoms, and contain oxygen, which is double-bonded to a carbon. Glucose is a simple six-carbon sugar that is the end-product of digestion of many complex carbohydrates, proteins, and fats. Glucose is manufactured by plants and is the main source of energy for most plants and animals. Common sugars that are isomers of glucose are galactose, which is derived from milk, and fructose, or fruit sugar.

Monosaccharides such as glucose and other six-carbon sugars, called hexoses, can join to form two-subunit disaccharides such as sucrose - table sugar (from glucose and fructose), and lactose - milk sugar, (from glucose and galactose), by removing a molecule of water from between each of the subunits in condensation reactions.