Endometriosis refers to the occurrence of endometrial tissue outside the uterine cavity, a common gynecological condition that often leads to painful menstruation, pain during intercourse, and infertility. Diagnosing endometriosis involves several approaches. First, inquire about the patient's clinical symptoms, including any painful menstruation and pain during intercourse. Second, a pelvic ultrasound should be performed to observe the situation inside the pelvis, assessing for any ovarian endometriotic cysts or pelvic endometriotic lesions. Third, a blood test for CA-125 can be conducted, as the levels of CA-125 tend to increase with endometriosis. Fourth, laparoscopy can be used to collect local tissue for pathological examination, which is the gold standard in diagnosing endometriosis.