The word "ecumenism" (ek-yoo-muh-niz-uhm) is derived from the Greek oikoumene, which means "the inhabited world". The term is usually used with regard to movements toward religious unity. In its most broad meaning therefore, ecumenism is the religious initiative towards world-wide unity. As a minimum, ecumenism is the promotion of unity, co-operation, or improved understanding between distinct religious groups or denominations within the same religion more or less broadly defined.
Two general types of ecumenism are discernible. The interfaith ecumenical movement strives for greater mutual respect, toleration, and co-operation between the world religions. Ecumenism in this sense is discussed at great length under the entry on religious pluralism. This is distinguishable from ecumenism within a faith-group.
One of important theoreticians of ecumenism was a French priest and theologian Yves Congar.