Stir frying is an umbrella term use to describe two fast Chinese cooking techniques: chǎo (炒) and bào (爆). The term stir-fry was introduced into the English language by Buwei Yang Chao, in her book How to Cook and Eat in Chinese, to describe the chǎo technique. The two techniques differ in their speed of execution, the amount of heat used, and the amount of tossing done to cook the food in the wok. Cantonese restaurant patrons judge a chef's ability to perform stir frying by the "wok hei" produced in the food. This in turn is believed to display their ability to bring out the qi of the wok.