Communicatio Essentiae is a Latin term that means communication of the essence. The term is used primarily to convey that the communication of the 'essence' or substance of the Godhead proceeds from the Father to the Son, and from both the Father and the Son to the Holy Spirit.
This theological stance is one of the factors in the East/West split in Christian tradition. This split is still seen between the Western Roman Catholic Church joined by the Protestants and the Eastern Orthodox Churches. The discussion of the Communicatio Essentiae factors into theological conversations about the authority of Christ, subordinationism and hierarchy within the Godhead.