Cheese is essentially curdled milk or cream. This means that the whey has been separated from the curds.

The whey is the liquid part of the milk. The curds are the solid part. Once the curds have separated from the whey, the whey ceases to be white in color and sometimes takes on a bluish appearance.

Milk curdled by using acid and rennet is considered to result in true cheese. Rennet is an enzyme that is naturally present in the fourth stomach of baby cows.

Milk curdled by using acid alone is not considered to produce true cheeses.

Whey protein is used to supplement the diets of some vegetarians. It is also used in protein supplements for athletes.

http://www.reflex-nutrition.com/en/whey-protein/