A Ghost Ship can be two completely different types of phenomena. 

On one hand a "ghost ship" can be an apparition of a ship that appears in a very similar way to a human ghost or spirit. I.e. It appears mysteriously, is semi-transparent, translucent, sometimes glowing, then vanishes without a trace. Such as the legend of the Flying Dutchman. Sometimes referred to as a "Phantom Ship".

The other kind of "ghost ship" is a real ship that is found adrift, derelict completely void of all crew. Presumed missing or dead. Such as the Mary Celeste. 



Painting of the Flying Dutchman Ghost Ship.