Peristalsis is the coordinated muscle contraction and relaxation that helps move food through the digestive tract [the long tube in the body where food goes after it is swallowed]. This process allows the body to break down and absorb nutrients from food. For example, peristalsis helps push food from the esophagus [the tube connecting the mouth to the stomach] into the stomach and then through the intestines [the long tube in the body where nutrients are absorbed] for further digestion and absorption.
Very Simple Definition:
Peristalsis is the squeezing and relaxing of muscles in our digestive system that helps move food through our bodies. For example, it helps push food from our throat into our stomach and then through our tummy tubes where our body takes out the good parts.