The term, from the Latin carnis ("flesh") literally means "enfleshment." It reflects the christological doctrine that Jesus was fully human and fully divine, the Son of God "in the flesh." It is based on Jn 1:14, "And the Word became flesh and lived among us."
During the first four centuries of the church, the nature of the relationship of divine and human in Jesus was hotly contested. The notion that Jesus, a mere human being, was "adopted" by God (Adoptionism); or that Jesus was purely God and merely seemed to have human form (Docetism); or that Jesus had two completely distinct natures, divine and human (Nestorianism); or that Jesus had a single divine nature (Monophysitism) were all rejected by general councils of the church. In contrast, the orthodox doctrine of the Incarnation recognized Jesus to be "truly God and truly man . . . in two natures, without confusion, without change, without division, without separation," as noted by the Council of Chalcedon (451) (BCP, p. 864).
Glossary definitions provided courtesy of Church Publishing Incorporated, New York, NY,(All Rights reserved) from “An Episcopal Dictionary of the Church, A User Friendly Reference for Episcopalians,” Don S. Armentrout and Robert Boak Slocum, editors.