Peristalsis is the muscular chain of events that moves everything through the human body. It begins with the muscular contractions that move food "down"
your esophagus even if you are hanging upside down and it ends with the muscular contractions of the anus to expel waste from the body.
Reverse Peristalsis is the extremely rare phenomenon that is the reversal of that process, which results in fecal matter being expelled through the mouth, etc.