Stir frying is a Chinese cooking technique commonly used in Chinese restaurants because of its fast cooking speed. Cantonese restaurant patrons judge the chefs by their "wok qi" (their ability to bring out the qi of the wok, which shows in the food as the look, smell and taste).
A round bottom pan called a wok is heated to very high temperature. Then, some oil is put in, followed by seasoning and the food items. The food is stirred and tossed very quickly using a big metal spatula. Some chefs will lift the wok to the side to let the flame light the oil, or a dash of wine spirit, on the food to give it extra flavor. Most dishes are cooked this way within 30 seconds.
Some dishes that require more time are cooked by adding a few dashes of water after the stirring. Then the wok is covered with a lid. As soon as steam starts to come out from under the lid, the dish is ready. In this case, the food is stir fried in high heat for the flavor and then steamed to make sure it is fully cooked.
Stir frying at home often cannot achieve the same great flavor as in restaurants mainly because the wok is not hot enough and the wok is too small to allow fast tossing. Most home kitchens are not equipped to handle the large amount of oil vapour produced as a byproduct of proper stir frying.
Many western cooks on TV demonstrate stir frying on low heat with a small wok and a stirring motion comparable to tossing a salad. This is a western adaptation of stir frying, but is dissimilar to the traditional Chinese method.