Any costume that resembles a ghost.
This may consist of a white sheet with eye holes cut out, or a white hooded cloak.
In addition to this, Japanese media often depicts ghosts in Buddhist burial clothing, called shinishozoku. This often includes a simple white kimono with a collar folded right-over-left to denote death, as well as a white triangular headpiece.
Characters might also be depicted alongside floating fire-shaped orbs called hitodama. The character might be also do a ghost pose by raising their hands and allowing their wrists to dangle loosely.