The simple sugars such as glucose or fructose are called monosaccharides. They are the building blocks for carbohydrates.

Here's a breakdown:

* Monosaccharides: These are the simplest forms of carbohydrates and cannot be broken down further into smaller sugar units. Examples include glucose, fructose, and galactose.

* Disaccharides: These are formed when two monosaccharides are joined together. Examples include sucrose (glucose + fructose), lactose (glucose + galactose), and maltose (glucose + glucose).

* Polysaccharides: These are complex carbohydrates formed by the joining of many monosaccharide units. Examples include starch, glycogen, and cellulose.

So, to answer your question directly, monosaccharides are the simple sugars that serve as the building blocks for all carbohydrates.