Presence of endometrial tissue within the myometrium is defined as

Endometriosis is defined as the presence of endometrial tissue (glands and stroma) outside the uterus. The most frequent sites of implantation arethe pelvic viscera and the peritoneum.Adenomyosis is defined as the presence of endometrial stroma and glands within the myometrium, at least one low-power field from the basis of theendometrium, whereas endometriosis is characterized by ectopic endometrium appearing within the peritoneal cavityRef: Berek and Novak&;s Gynecology; 15th edition; Chapter 17