Natalie

pretty sure in order to be a ghost one has to be unalive

No because undead have bodies imo

they're just dead IMO

Depends on your definition of “undead” I think. Per Merriam-Webster’s “not dead : returned from or as if from death,” unquestionably yes. Per Oxford’s “dead, but still able to move, act and (in some cases) think and speak,” a bit of a harder call but arguably yes since they can move and act even though their form is incorporeal. Per Dictionary.com’s “no longer alive but animated by a supernatural force,” probably not because a ghost is arguably the supernatural force itself doing the animating

If it takes extra damage from blunt weapons or clerics, then it's undead.

they're considered undead in yugioh (though the English translation uses "zombie" instead of "undead" for whatever reason)

i personally would say absolutely! the whole point of "undead" is something neither living nor dead--hence needing a new term--and ghosts are arguably the archetypical tale of spirits trapped between life and death. I can't imagine a useful general definition that excludes them, outside obviously of specialized setting stuff.