What is the medical condition known as a rectal prolapse?

The rectum is the lowest part of the GI tract. Basically where the stool collects before being expelled. A prolapse is where it "falls" or comes out. this means that, usually because of pushing hard, some of the rectum will be outside the anus and visible. It is them carefully reinserted and stool softeners are often used to keep the stools soft and prevent another occurance. It is more common with weakened muscles, usually from age, or perhaps a traumatic childbirth.

not sure but rectal is your back bum and prolapse does that not mean dropped?

it's when your rectal loses it's mucles tension and like gets saggy. this can happen later in life after you've had anal sex for most of your adult life. people don't think anal sex has any consequences, but it does. other things can cause rectal prolapse as well.

Rectal prolapse normally describes a medical condition wherein the walls of the rectum protrude through the anus and hence become visible outside the body. There are three chief conditions which come under the title rectal prolapse:

Full-thickness rectal prolapse describes the entire rectum protruding through the anus
Mucosal prolapse describes only the rectal mucosa (not the entire wall) prolapsing
Internal intussusception wherein the rectum collapses but does not exit the rectum

Causes
It is caused by weakness of the pelvic floor muscles and descending of the pelvic floor organs (uterus) - this is why the condition is most common among middle-aged to elderly women (women account for 85% of all reported conditions*). It is often accounted to chronic abdominal straining (notable in pregnancy, constipation) and anal sex.

The slang term "pink sock" is used to refer to when the rectum is accidentally pulled out during anal sex due to a variety of factors including insufficient lubrication and a much larger than average diameter penis.

Additionally, infection with whipworm can weaken these muscles and cause rectal prolapse in children.

Progression
The condition undergoes progression: beginning with prolapsation during bowel movements, through Valsalva movements (sneezing and so forth), then through daily activities such as walking until finally it may become chronic and cease to retract.

Treatment
Pharmaceutically, the condition may only be treated secondarily (by treating deficate) so as to avoid further straining.

The alternative, of course, is surgery, it may be divided into two forms of procedure: abdominal surgery and perineal surgery.

Abdominal surgery - for younger patients, but is more dangerous
Anterior resection
Marlex rectopexy
Suture rectopexy
Resection rectopexy

Perineal surgery - often performed on older patients and is less dangerous
Anal encirclement
Delorme mucosal sleeve resection
Altemeier perineal rectosigmoidectomy
Hemorrhoidectomy

Children are treated with linear cauterization