Ecumenism or oecumenism now mainly refers to initiatives aimed at greater religious unity or cooperation.
In its broadest sense, this unity or cooperation may refer to a worldwide religious unity; by the advocation of a greater sense of shared spirituality across the three Abrahamic faiths of Judaism, Christianity and Islam. Most commonly, however, ecumenism is used in a more narrow meaning; referring to a greater cooperation among different religious denominations of a single one of these faiths.
The word is derived from Greek οἰκουμένη (oikoumene), which means "the inhabited world", and was historically used with specific reference to the Roman Empire. Today, the word is used predominantly by and with reference to Christian denominations and Christian Churches separated by doctrine, history, and practice. Within this particular context, the term ecumenism refers to the idea of a Christian unity in the literal meaning: that there should be a single Christian Church.