In a comprehensive sense, the Holy Ghost is the third member of the Godhead. As the name (or title) suggests, the Holy Ghost is a personage of Spirit, not having a body of flesh and bones. (D&C 130:22)
In God’s Plan of Salvation, “Holy Ghost” is a Priesthood calling or assignment. Just as many priesthood assignments or offices within the Church possess “titles” (i.e. President, Prophet, , Apostle, Elder, Brother, Sister, etc.), so too, do positions in the godhead contain titles of distinction (i.e. Father, Son, and Holy Ghost). The individual holding the position of the third member of the godhead has a name, and, that name is not Holy Ghost. It is a position of Authority.
The calling of an Holy Ghost is one of high-proportion, appointed-omnipotence and omnipresence. Under the Supreme Key Holder, an Holy Ghost administers assigned tasks through delegated keys. The model is replicated in the Lord’s Church as well, through His authorized leaders on earth. This model (Perpetual Plan) is also duplicated in innumerable Kingdom’s throughout the expanse of space. (D&C 88:36-39)
What is “Holy.” A common use definition is: exalted or worthy of complete devotion as one perfect in goodness and righteousness.
I would suggest, that although the Holy Ghost is perfect in purpose and perfect through covenant, he has not yet been “perfected,” (as our Heavenly Father has) the culmination of a process that he will achieve following his mortal probation. (D&C 93:33, and see: Words of the Prophet Joseph Smith, p. 245, Nauvoo, 27 August 1843.)
What is “Ghost.” A common use definition is: A disembodied soul. (https://www.merriam-webster.com/dictionary/ghost)
However, I would suggest the more complete definitional explanation is this: “The spirit and the body are the soul of man.” (D&C 88:15) Because the Holy Ghost is a pre-mortal spirit, he is not disembodied, because he is not yet a “living soul.” (Temple verbiage, and Moses 3:7)
The Holy Ghost is in an unembodied spirit state (aka pre-mortal spirit), or, a spirit that has not yet taken on a body of flesh and bones through the process of mortal birth. Once born, spirit matter and hamburgers, or pizza, or, fill in the blank HERE with your favorite fast-food (aka earthly elemental matter), join together to create a body, and are considered “alive.” When the spirit and the fast-food body separate, a person is considered “dead.” The person’s spirit then becomes “disembodied.”
In God’s Plan, a person who has died, and then is resurrected, becomes a re-embodied spirit—inseparable and glorified. (“Glorified” only applies to persons who receive a kingdom of glory, see D&C 76:51-70 (Celestial); D&C 76:71-80 (Terrestrial); D&C 76:81-86 (Telestial); D&C 76:32-38 (Sons of Perdition))
The definition of “ghost” is more accurately: An unembodied spirit if you haven’t been born yet, or a disembodied spirit if you’ve lived and then died, and not yet lived again (in which case you’d be resurrected, or re-embodied).
So, an Holy Ghost is the third member of the godhead, who has accepted, and is fulfilling, a priesthood assignment under delegated keys, who is one worthy of worthy of complete devotion as one perfect in goodness and righteousness within the covenant (which covenant of the Perpetual Family we will discuss later), and is currently in an unembodied state.
