Well here is the WebMD definition:

Endometriosis is a disease in which cells that look and act like the cells that line the uterus (endometrial cells) are found in other locations in the body, usually in the pelvis. These cells can attach to the ovaries or fallopian tubes; the outer surface of the uterus, the bowels, or other abdominal organs; or, rarely, to other organs and structures in the body. The places where the cells attach are called implants, or lesions.

Endometrial cells that are found outside the uterus respond to hormones released during the menstrual cycle in the same way as endometrial cells that are located in the uterus.1 At the beginning of the normal menstrual cycle, when the lining of the uterus is shed and menstrual bleeding begins, the sites of these abnormally located cells (implants) may swell and bleed.

The body responds to the swelling and bleeding by surrounding the cells with scar tissue. During the menstrual cycle, this scar tissue may become red, swollen, and painful. As the scar tissue increases, it can form adhesions that cover and bind the abdominal organs. Adhesions can interfere with an organ's normal function.

http://my.webmd.com/hw/endometriosis...000_1077_00_07

Maybe back when you were diagnosed they called the cells 'metriosis'?