Whey is a liquid byproduct that comes from the process of making cheese. When milk is curdled, it separates into solid curds and liquid whey. This liquid is rich in protein and contains essential amino acids, making it a popular ingredient in many protein supplements and health foods. Many athletes and fitness enthusiasts use whey protein to help build muscle and recover after workouts. It can be found in various forms, such as whey protein concentrate, whey protein isolate, and whey protein hydrolysate, each differing in protein content and processing methods.