Ecumenism is any effort aimed at the unity of Christians throughout the world. Most often, it specifically means the visible unity of Christian churches in some form. The adjective ecumenical can also be applied to any interdenominational initiative that encourages greater cooperation among Christians and their churches, whether or not the specific aim of that effort is full, visible unity. The terms "ecumenism" and "ecumenical" come from the Greek (oikoumene), which means "the whole inhabited world", and was historically used with specific reference to the Roman Empire. The ecumenical vision comprises both the search for the visible unity of the Church (Ephesians 4:3) and the "whole inhabited earth" (Matthew 24:14) as the concern of all Christians.
In Christianity the qualification ecumenical is originally (and still) used in terms such as "Ecumenical council" and "Ecumenical patriarch" in the meaning of pertaining to the totality of the larger Church (such as the Catholic Church or the Orthodox Church) rather than being restricted to one of its constituent local churches or dioceses. Used in this original sense, the term carries no connotation of re-uniting the historically separated Christian denominations, but presumes a unity of local congregations in a worldwide communion.