The Holy Spirit, or Holy Ghost is God, the third Person of the Holy Trinity. The Holy Spirit is co-equal with the Father and the Son. The word "Spirit" commonly translates the Greek New Testament word pneuma.
The Spirit dwells inside every true Christian, each one's body being his temple (First Epistle to the Corinthians 3:16). He is depicted as a 'Counsellor' or 'Helper' (paraclete in Greek, guiding them in the way of the truth. The 'Fruit of the Spirit' (i.e. the result of his work) is "love, joy, peace, patience, kindness, goodness, faithfulness, gentleness and self-control" (Galatians 5:22). The Spirit is also believed to give gifts (i.e. abilities) to Christians.
Christians believe that it was the Holy Spirit whom Jesus mentioned as the promised "Comforter" (i.e. "strengthener", "fortifier") in John 14:26. After his resurrection, Christ told his disciples that they would be "baptized with the Holy Ghost", and would receive power or endowment (Acts 1:4-8); a promise that was fulfilled in the events recounted in the second chapter of Acts. On the first Pentecost, Jesus' disciples were gathered in Jerusalem when a mighty wind was heard and tongues of fire appeared over their heads. A multilingual crowd heard the disciples speaking, and each of them heard them speaking in his or her native language.
"Holy Spirit" or "Holy Ghost"
Holy Ghost was the common name for the Holy Spirit in English prior to the 20th century. It is the name used in the King James Version of the Bible, and is still used by those who prefer more traditional language. The word ghost has lost its old meaning of the spirit or soul that is inside man and come to be identified almost exclusively with the concept of disembodied spirits, usually of the dead, which may "haunt" the living, an idea far from that intended by the King James translators.
Depiction in art
The Holy Spirit is often depicted as a dove, based on the account of the Holy Spirit descending on Jesus in the form of a dove when he was baptized in the Jordan River. The book of Acts describes the Holy Spirit descending on the apostles at Pentecost in the form of a wind and tongues of fire resting over the apostles' heads. Based on the imagery in that account, the Holy Spirit is sometimes symbolized by a flame of fire.