“A woman’s uterus is lined with endometrial tissue. This lining is called the endometrium. Your body grows a new endometrium with each menstrual cycle to prepare for a fertilized egg. Endometriosis is a condition in which endometrial tissue grows outside the uterus.  Endometriosis affects up to 10% of women between the ages of 15 and 44. It most often occurs on or around reproductive organs in the pelvis or abdomen and grows outside the uterus. The buildup of abnormal tissue outside the uterus can lead to inflammation, scarring and painful cysts. It can also lead to buildup of fibrous tissues between reproductive organs that causes them to “stick” together.”

John Hopkins Medicine (https://www.hopkinsmedicine.org/health/conditions-and-diseases/endometriosis)