In Christian terminology, docetism (from the Greek δοκεῖν/δόκησις dokeĩn (to seem) dókēsis (apparition, phantom), according to Norbert Brox, is defined narrowly as "the doctrine according to which the phenomenon of Christ, his historical and bodily existence, and thus above all the human form of Jesus, was altogether mere semblance without any true reality." Broadly it is taken as the belief that Jesus only seemed to be human, and that his human form was an illusion. The word Δοκηταί Dokētaí (illusionists) referring to early groups who denied Jesus' humanity, first occurred in a letter by Bishop Serapion of Antioch (197–203), who discovered the doctrine in the Gospel of Peter, during a pastoral visit to a Christian community using it in Rhosus, and later condemned it as a forgery. It appears to have arisen over theological contentions concerning the meaning, figurative or literal, of a sentence from the Gospel of John: "the Word was made Flesh".
Docetism was unequivocally rejected at the First Council of Nicaea in 325 and is regarded as heretical by the Catholic Church, Orthodox Church, and Coptic Church.
Docetism is broadly defined as any teaching that claims that Jesus' body was either absent or illusory. The term 'docetic' should be used with caution, since its use is rather nebulous. For Robert Price "docetism", together with "encratism", "Gnosticism" and "adoptionism", has been employed "far beyond what historically descriptive usage would allow". Two varieties were widely known. In one version, as in Marcionism, Christ was so divine that he could not have been human, since God lacked a material body, which therefore could not physically suffer. Jesus only appeared to be a flesh-and-blood man; his body was a phantasm. Other groups who were accused of docetism held that Jesus was a man in the flesh, but Christ was a separate entity who entered Jesus's body in the form of a dove at his baptism, empowered him to perform miracles, and abandoned him upon his death on the cross.