The Holy Spirit is a term often used to refer to the Holy Ghost. To members of The Church of Jesus Christ of Latter-day Saints, sometimes casually called "Mormons," the two terms (Holy Spirit and Holy Ghost) are used synonymously. Ghost is an Old English word meaning spirit. The scriptures use the term Holy Spirit to designate the third member of the Godhead and to speak of the Spirit's power to testify, to grant knowledge, to persuade, to indicate remission of sins, and to sanctify.
Also see: Holy Ghost