What condition is characterized by the presence of endometrial tissue outside the uterus?

Endometriosis is a condition where tissue similar to the endometrium, which normally lines the uterus, grows outside of it. This ectopic endometrial tissue can be found on the ovaries, fallopian tubes, the outer surface of the uterus, and other organs within the pelvis. This abnormal placement of endometrial tissue can lead to inflammation, pain, and other symptoms such as heavy menstrual bleeding and infertility.

In contrast, uterine fibroids are non-cancerous growths of the uterine muscle and do not involve the presence of endometrial tissue outside the uterine cavity. Pelvic inflammatory disease (PID) is an infection of the female reproductive organs and is associated with sexually transmitted infections, but it is not characterized by endometrial tissue outside the uterus. Ovarian cysts are fluid-filled sacs that develop on the ovaries, but again, they are not related to the presence of endometrial tissue outside of its normal location. Thus, endometriosis specifically describes the presence of endometrial-like tissue outside the uterus, making it the correct answer.