What process refers to the decomposition of body tissues and is considered a definitive sign of death?

The decomposition of body tissues referred to in the question is known as putrefaction, which is indeed considered a definitive sign of death. Putrefaction occurs when the body's cells break down and the tissues begin to decompose due to the action of bacteria and other microorganisms. This process results in the characteristic changes in the body, such as discoloration and the production of gases, which can create a foul odor.

Putrefaction is inevitable once the body has ceased all biological functions, making it a reliable indicator that death has occurred. It typically starts soon after death and continues for days and weeks, depending on various factors such as the environment and the condition of the body.

Other processes mentioned, such as rigor mortis, which refers to the stiffening of muscles after death, cadaveric spasm, which is an immediate stiffening of muscles that can occur at the time of death, and necrosis, which is the death of body tissue that can be a result of many factors, do not signify the overall decomposition of body tissues in the same definitive way that putrefaction does.