Yūrei are figures in Japanese folklore analogous to the Western concept of ghosts. The name consists of two kanji, 幽 (yū), meaning "faint" or "dim" and 霊 (rei), meaning "soul" or "spirit". Alternative names include Bōrei (亡霊), meaning ruined or departed spirit, Shiryō (死霊), meaning dead spirit, or the more encompassing Yōkai (妖怪) or Obake (お化け). Like their Chinese, Korean, and Western counterparts, they are thought to be spirits barred from a peaceful afterlife.

Yōkai are a class of supernatural entities and spirits in Japanese folklore. The word yōkai is composed of two kanji characters that both mean "suspicious, doubtful", and while it may be regarded as a loanword from the Chinese term yaoguai, the word yōkai has taken on multiple different meanings particular to a Japanese context.