Complex sentence: In hierarchical Christian churches, especially Eastern Orthodox and Oriental Orthodox churches, when a high-ranking bishop, such as a patriarch, releases an ecclesiastical province from his authority while remaining in full communion with that newly independent church, he is granting autocephaly.
Split into simpler sentences: In hierarchical Christian churches, especially Eastern Orthodox and Oriental Orthodox churches, autocephaly is the status of a hierarchical church whose head bishop does not report to any higher-ranking bishop. When a high-ranking bishop, such as a patriarch, releases an ecclesiastical province from his authority while remaining in full communion with that newly independent church, he is granting autocephaly.