This is called a rectocele.
A rectocele occurs when the end of the large intestine (rectum) pushes against and moves the back wall of the vagina. An enterocele (small bowel prolapse) occurs when the small bowel presses against and moves the upper wall of the vagina. Rectoceles and enteroceles develop if the lower pelvic muscles become damaged by labor, childbirth, or a previous pelvic surgery or when the muscles are weakened by aging. A rectocele or an enterocele can be present at birth (congenital), though this is rare.