Terminology
Prolapse refers to "the falling down or slipping of a body part from its usual position or relations". It is derived from the Latin pro- - "forward" + labi - "to slide". Merriam-Webster Dictionary Prolapse Prolapse can refer to many different medical conditions other than rectal prolapse.
procidentia has a similar meaning to prolapse, referring to "a sinking or prolapse of an organ or part". It is derived from the Latin procidere - "to fall forward". Procidentia usually refers to uterine prolapse, but rectal procidentia can also be a synonym for rectal prolapse.
Intussusception is defined as invagination (infolding), especially referring to "the slipping of a length of intestine into an adjacent portion". It is derived from the Latin intus - "within" and susceptio - "action of undertaking", from suscipere - "to take up". Merriam-Webster Dictionary Intussusception Rectal intussusception is not to be confused with other intussusceptions involving colon or small intestine, which can sometimes be a medical emergency. Rectal intussusception by contrast is not life threatening.
Intussusceptum refers to the proximal section of rectal wall, which telescopes into the lumen of the distal section of rectum (termed the intussuscipiens). What results is 3 layers of rectal wall overlayed. From the lumen outwards, the first layer is the proximal wall of the intussusceptum, the middle is the wall of the intussusceptum folded back on its self, and the outer is the distal rectal wall, the intussuscipiens.
Read more about this topic: Internal Intussusception