Stir-fry cookers are typically woks, which are large, round-bottomed cooking vessels that originated in China. Woks are used to quickly cook food over high heat, making them ideal for stir-frying. They are also versatile enough to be used for steaming, deep-frying, boiling, and braising. The shape of the wok allows for even heat distribution and efficient use of space, making it a popular choice for stir-fry cooking.