The theological system of Plotinus (c205-270) and his successors, who included Porphyry, Iamblichus, and Proclus.  Its basic characteristic is the doctrine of the three hypostases: the One, the ultimate unknowable source from which everything exists emanates; Intelligence, the realm of perfective intuitive knowledge; and Soul, the realm of discursive thought.  The outward movement of emanation is met by the ascending movement of return, which manifests itself as ‘contemplation’; everything that exists is a balance between these two forces.  The contemplative movement of return seeks the One by purification, which for the intellect means a method of abstraction, and finds union with the One in a mystical experience of ecstasy.

Thoroughgoing Neoplatonists were necessarily hostile to Christianity, but Neoplatonism influenced Christian theology, partly through its diffusive impact on the whole Roman world.  Its influence is apparent in the writings of St. Augustine, Synesius, and Dionysius the Pseudo-Areopagite.

Taken from: The Concise Oxford Dictionary of the Christian Church, Ed. Livingstone. Dr. E. A. 2006, entry “Neoplatonism” p. 405, pub. Oxford University Press