Wiktionary
alt. A paper stock that is thicker and more durable than normal writing paper or printing paper, but thinner and more flexible than other forms of paperboard, used for postcards, playing cards, etc. n. A paper stock that is thicker and more durable than normal writing paper or printing paper, but thinner and more flexible than other forms of paperboard, used for postcards, playing cards, etc.
Wikipedia
Card stock, also called cover stock or pasteboard, is a paper stock that is thicker and more durable than normal writing or printing paper, but thinner and more flexible than other forms of paperboard.
Card stock is often used for business cards, postcards, playing cards, catalogue covers, scrapbooking, and other uses which require higher durability than regular paper. The texture is usually smooth, but can be textured, metallic, or glossy. When card stock is labeled as cover stock it often has a coated finish on one side or both sides (C1S or C2S, for Coated: One Side, or Coated: Two Sides) to produce a glossy look and smooth texture, especially in use for the printing of business cards and book covers.
Usage examples of "card stock".
By means of a magical proprietary process that 3M has sworn me never to reveal, the bubbles are then conveyed into a plastic goo, which can then be used like ink and printed onto (preferably) some sort of stiff card stock with a modified printing press.
With a finely ground pen point he printed an exact duplicate of the invitation on heavy card stock.
The card stock felt handmade and the words had the smudgy edges of rubber stamp printing.