• Noun: a mental representation of some haunting experience; examples: "he looked like he had seen a ghost", "it aroused specters from his past"
• Noun: a writer who gives the credit of authorship to someone else
• Noun: the visible disembodied soul of a dead person
• Noun: a suggestion of some quality; examples: "there was a touch of sarcasm in his tone", "he detected a ghost of a smile on her face"
• Verb: move like a ghost; example: "The masked men ghosted across the moonlit yard"
• Verb: haunt like a ghost; pursue; example: "Fear of illness haunts her"
• Verb: write for someone else; example: "How many books have you ghostwritten so far?"
A ghost is someone who hasn't made it - in other words, who died, and they don't know they're dead. So they keep walking around and thinking that you're inhabiting their - let's say, their domain. So they're aggravated with you.