From BiblePortal Wikipedia

Heresies of the Church Thru the Ages [1]

Nestorius, Patriarch of Constantinople (5th century), while combating the Arians, came to accept the view that in Christ the two natures stand for two personalities which are united in one moral person. This doctrine had previously been prevalent in the School of Antioch where it was held by Diodorus of Tarsus and Theodore of Mopsuestia of whom Nestorius was the disciple. Like his master, Nestorius refused to admit that Mary was the Mother of God, but claimed she was only the mother of Christ. He was condemned by the aecumenical councils of Ephesus (431) and Chalcedon (451). Many of his followers persistently adhered to their beliefs and formed a powerful religious body, part of which has survived to our own day.

Webster's Dictionary [2]

(n.) The doctrines of the nestorian Christians, or of Nestorius.