In the Eastern Orthodox Churches, a metropolis (also called metropolia or metropolitanate) is a type of diocese, along with eparchies, exarchates, and archdioceses. In the Churches of Greek Orthodoxy (Church of Greece, Greek Orthodox Archdiocese of America, etc.), every diocese is a metropolis, headed by a metropolitan: auxiliary bishops are the only non-metropolitan bishops. In non-Greek Orthodox Churches, mainly Slavic, the title of metropolitan is given to the heads of autocephalous Churches or of a few important episcopal sees.
In the Eastern Catholic Churches, a metropolitanate is an autonomous Church of a lower category than the patriarchal and the major archiepiscopal Churches and is headed by a single metropolitan of a fixed episcopal see.