In Christianity, the third person of the Holy Trinity. Though references to the spirit of Yahweh (God) abound in the Old Testament, Christian teaching about the Holy Spirit is derived mainly from the Gospels. The Holy Spirit descended on Jesus at his baptism, and outpourings of the Spirit are mentioned in the Acts of the Apostles, in which healing, prophecy, exorcism, and speaking in tongues are associated with its activity. The Holy Spirit also came to the disciples during Pentecost. The definition of the Holy Spirit as a divine person equal in substance to the Father and the Son was made at the Council of Constantinople (AD 381).