Supernatural is probably one of the first words an individual pictures when thinking about the word ghost; however, a ghost is simply someone or something that goes by unseen.
In a large company, there are many ghosts working behind the scenes to pull the strings that ensures everything functions properly.
In a large family, a child might think of themselves as a ghost as they receive less attention than their siblings.
And then there's the version that everyone thinks of first: the souls of the recently deceased with unfinished business, unable to move on to the afterlife.