Blue crab (Callinectes sapidus — Latin for "beautiful savory swimmer") is a crustacean native to the western Atlantic, especially the Chesapeake Bay, where it has long been a food source for coastal communities. Its sweet, delicate, slightly briny meat comes from the body and claws.
Blue crab is central to Mid-Atlantic and Gulf Coast American cooking, appearing in crab cakes, deviled crab, crab dip, and seafood chowder, usually seasoned with Old Bay or citrus. It also turns up in Asian stir-fries, soups, and steamed dishes, and in Italian and Mediterranean pasta, risotto, and seafood salads.
Atlantic blue crab is a different species from the blue swimmer crab of the Indo-Pacific (Portunus armatus), despite the similar common names and comparable size and flavor; the two aren't interchangeable in a recipe calling for one specifically, though either works in dishes that simply call for crab meat.
Live blue crabs should feel heavy for their size with intact shells; the meat is highly perishable and best cooked soon after purchase.