what is the difference between pentose sugar and sugar???

Sugar is an informal term for a class of edible crystalline substances, mainly sucrose, lactose, and fructose characterized by a sweet flavor. In food, sugar almost exclusively refers to sucrose, which primarily comes from sugar cane and sugar beet. Other sugars are used in industrial food preparation, but are usually known by more specific names—glucose, fructose or fruit sugar, high fructose corn syrup, etc.

It can have any number of carbon atoms.

A pentose sugar is a monosaccharide with 5 carbon atoms. Example is ribose