The One, Holy, Catholic and Apostolic Church is the Orthodox Church of Jesus Christ, against which he promised the gates of hell would not prevail. Specifically, one, holy, catholic, and apostolic Church is the creedal form of belief in the Church. What is implied in that belief are commonly called the attributes of the Church: unity, sanctity, catholicity, and apostolicity. (OrthodoxWiki)

The Church is the Body of Christ, a theanthropic (divine-human) communion of Jesus Christ with his people. The sole head of the Church is Christ. The Church is an object of faith, that is, Orthodox Christians believe in the Church. The traditional belief in the Church is attested to in the Nicene-Constantinopolitan Creed as the one, holy, catholic and apostolic Church. By this phrase is meant that the Church is undivided and not many (one), sanctified and set apart for the work of God (holy), whole and characterized by fullness and universality (catholic), and has at its essence the going out into all the world to preach the Gospel and baptize the nations (apostolic). (OrthodoxWiki)