Card stock, also called cover stock, is a stiff or rigid paper stock. Card stock is often used for postcards, catalog covers, scrapbooking, and other uses which require rigidity. The texture is usually smooth, but can be textured, metallic, or glossy.
Card stock thickness is often described by pound weight. Pound weight is the weight of 500, 20" by 26" sheets. This differs from how text stock is determined, which assumes 500, 25" by 38" sheets.
In the US, card stock thickness is usually measured in points or mils that gives the thickness of the sheet in thousandths of an inch. For example, a 10 pt. card is 0.010" thick; 12 pt. is 0.012".