All those carbohydrates which contain a free aldehyde or ketonic group and reduce Fehling's solution and Tollen's reagent are referred as a reducing sugar. Examples of reducing sugar are galactose, glucose, glyceraldehyde, fructose, ribose, and xylose.
Non-reducing sugars do not have an $\mathrm{OH}$ group attached to the anomeric carbon so they cannot reduce other compounds. All monosaccharides such as glucose are reducing sugars. Examples Sucrose, Trehalose, Raffinose, Stachyose.
A Caution
$\Rightarrow$ The anomeric carbon is the carbon derived from the carbonyl carbon compound (the ketone or aldehyde functional group) of the open-chain form of the carbohydrate molecule. The anomeric carbon can be determined by the carbon attached to two oxygen atoms joined by single bonds.