Carding is an automated bot attack on an ecommerce store. Carders, such as Fullzforsale and Dumpswithpinshop, use various techniques to test card numbers against different payment processes to get valid card info. There are carding forums and websites (e.g. Dumpsshoponline and Cardingdumps) that share card numbers. Over time, when one forum gets shut down, carders turn to another.
These forums often have strict invitation rules, and organizers can identify security researchers. Carders usually aim at countries where most people use credit cards, with the US being one of the biggest markets.