what does it means to have ghosts?

Not sure of the context you are asking it, but if it is not a literal meaning of paranormal ghosts, then it usually refers to one being haunted by the past, whether it be someone you loved and lost, or not even someone but something you carry with you like a negative memory.

If let's say your partner says you have ghosts in your bed, I think it's reference to past partners you may have been with.

They could have Call Of Duty Ghosts, most commenly known by the name of Ghosts.

I think it may be a reference to having really pale skin after being frightened. Like when someone gets scared and their friend asks them, "What's wrong with you? You look like you've seen a ghost".

don't know