The adjective ecumenical refers to something universal, or something that has a wide, general application.
You might refer to a wide assortment of ethnic foods served together as being ecumenical, and you'd be technically correct, as the word does mean something general and worldwide. But the term is most widely connected with religious unity, specifically Christianity. The original Greek root word, oikos, means "house," and that grew into the word oikoumenikós, which means "the entire world." Today it most often refers to bringing people of diverse Christian religions together; however, an ecumenical service might bring Christians, Jews, and Muslims together under one roof.