**2. Definition of endometriosis**

Endometriosis is the presence of tissue resembling endometrial components outside the uterus. Usually both, glands and stroma are observed but occasionally the diagnosis can be made when only one component is present. Endometriosis is distinct from adenomyosis or endometriosis interna which is defined by the presence of endometrial components in the myometrium. These two entities were linked in the past by common terminology but present different clinical presentation, epidemiologic and etiologic patterns.
