Rigor mortis is the medical term for what happens to a body after death — its muscles and joints become very stiff. Every single muscle in the body is affected by rigor mortis. At the moment of death, the body of a person or an animal is loose and relaxed, but rigor mortis sets in about two hours later and lasts for several days. Even internal organs are stiffened by rigor mortis. The degree of rigor mortis in a body can give clues about what time death occurred. In Latin, rigor mortis literally means "the stiffness of death."

Source: Vocabulary.com