Organization of the Eastern Orthodox Church
The Eastern Orthodox Church is a communion comprising the collective body of sixteen separate autocaphalous hierarchical churches that are recognized or "canonical" parts of Eastern Orthodoxy. The head of the communion is the Patriarch of Constantinople, who is also head of one of the sixteen churches. The sixteen organizations are in full communion with each other, so any priest of any of those churches may lawfully minister to any member of any of them, and no member of any is excluded from any form of worship in any of the others. Despite the fact that, like the Roman Catholic church, they are "closed communion" churches, i.e. with rare exceptions excluding non-members from receiving the Eucharist, they admit each other's members to that sacrament. Friction among them is over matters of church politics rather than doctrine.
Like the Roman Catholic Church, the Eastern Orthodox Church claims to be the One Holy Catholic and Apostolic Church.
[Maybe the sixteen could be listed here.]