Stir-frying is similar to sautéeing, but amplified. With stir-frying, the heat is higher and the action is faster.
Sautéeing cooks large or small pieces of food in a wide, shallow pan in a small amount of hot fat over medium-high heat, turning often or just once. The fat may be a combination of butter and oil.
Stir-frying increases the heat to high, and keeps the food in constant motion. The pan commonly used is a round-sided wok. The food is continuously turned, tossed, and stirred. Butter is not used because it burns easily at high heat. Food is cut in small, thin pieces for fast-paced cooking.