In moern English, the term ghost ship has come to denote at least one of three separate (though occasionally overlapping) definitions, all of which involving, in one respect or other, unexplained circumstances. Historically, the term has been used to refer to reported sightings of apparitions over water that have appeared in the form of maritime sailing ships, often after having previously been known to have sunk, or to derelict vessels found floating with no crew. In fiction, ghost ships have often been vessels crewed by some manner of spectral or non-living beings.