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An Ecumenical council (or oecumenical council; also general council) is a conference of the bishops of the whole Church convened to discuss and settle matters of Church doctrine and practice. The word derives from the Greek language "Οικουμένη", which literally means "inhabited", and was originally a figure of speech referring to the territory of the Roman Empire since the earliest councils were all convoked by Roman Emperors. In later usage it was applied in a more general way to mean all places that are inhabited by human beings, therefore "world-wide" or "general." The acceptance of historical councils varies widely between different branches of Christianity.

"The whole church" is constructed by most Eastern Orthodox Christians as including all Eastern Orthodox jurisdictions in full communion with each other. This does not include the Roman Catholic/Eastern Catholic Churches, nor the Oriental Orthodox Churches. While a few Eastern Orthodox would see a council as fully ecumenical only if it included all the ancient patriarchates, including Rome, this is not mainstream Eastern Orthodox opinion. Similarly, Roman Catholics take the whole church to mean "only" those in full communion with the Bishop of Rome. Again, some Roman Catholics would see it necessary to include the Eastern Churches in an ecumenical council, in the full and proper sense. As Pope John Paul II often put it, the Church needs to breathe "with its two lungs" (referring to the Eastern Rites of the Catholic Church in union with Rome). More local meetings are sometimes called "synods", but the distinction between a synod and a council is not hard and fast. However, both churches, and many Protestants, do recognize the validity of the "Seven Ecumenical Councils", with the exception of the Quinisext Council which is rejected by Roman Catholics but considered part of the 6th council by the Eastern Orthodox.

The Greek word "synod" (σύνοδος) derives from "syn" (in Greek: σύν; in English: together) and "odos" (in Greek οδος; in English: road, way), therefore a synod is the coming together of several people sharing a common element, in this case the Christian bishops.

The Acts of the Apostles records the Council of Jerusalem, which addressed the tension between maintaining Jewish practices in the early Christian community with Gentile converts. Although its decisions are accepted by all Christians and later definitions of an ecumenical council appear to conform to this sole biblical Council, no Christian church includes it when numbering the ecumenical councils.