Final answer:
Atrophy refers to the wasting away and decrease in the size of a muscle, which occurs when a muscle is not being used or is immobilized for a prolonged period of time.
Step-by-step explanation:
Atrophy refers to the wasting away and decrease in the size of a muscle. It occurs when a muscle is not being used or is immobilized for a prolonged period of time. For example, muscle atrophy can happen when a limb is in a cast or when someone experiences a prolonged period of bed rest.