Adenomyosis refers to a disorder or problem that someone has due to there being something in the inside of the uterus that should not be there. This problematic thing that is in the inside of the uterus is called endometrial tissue. Endometriosis could happen when this disorder takes place, but sometimes they can happen separately. Endometriosis is when the cells grow outside of the uterus.
The key difference between the adenomyosis and endometriosis is that the first disorder is when the tissues are grown in the uterus and the second disorder is when the cells are grown outside of the uterus. One is grown inside and one is grown outside. Also, one grow tissue and the other grows cells that should not be there.