In Mormonism, the Holy Spirit or " Holy Ghost," is the third person of the Godhead, whose special mission is to guide and teach, testify to God, and comfort and sanctify human souls. He is "one in purpose with the Father and the Son, but is a separate being"  rather than an aspect of God or part of a Trinity. The Holy Ghost is pure spirit and has no body, unlike heavenly father and Jesus. "the Holy Ghost has not a body of flesh and bones, but is a personage of Spirit. Were it not so, the Holy Ghost could not dwell in us." 
- - "Who is the Holy Ghost?" Mormon.org.
- Doctrine and Covenants 130:22