Defining a Ghost

Years ago I started pecking away at the many different accounts of ghosts and separated them into my study categories.

Do any of you see other categories that wouldn't fit below these top-level zones for cataloging ghost phenomena?

• The actual deceased
  
• Entities / Other Life Forms
  
• Hallucinations (quite often the case)
  
• History Repeating Itself (static repitition, most "hauntings")
  
• Self-Generated Tulpa/Poltergeists or Intent Forms (some "hauntings")
  
• Trapped Portions of People in Objects (usually interactive, non-static, some "hauntings")
  
• Astral Projections of The Living
  

I'm really agnostic on this one.  I know full well  that the experience that we refer to as a ghost is a real experience, but what exactly is causing it I haven't a clue.  I would define a ghost as "that to which we assign the properties of a ghost."