Yokai
Demons

for further reading: Wikipedia

The term "yokai" essentially is a catch-all term for any sort of magical or mythical Japanese creature including oni, kappa, yuki-onna, tsukumogami, tanuki and kitsune.

Humans are also capable of become yokai by a variety of means. Jealous women supposedly transformed into oni, while other humans may become rokuro-kubi (humans with extremely long necks) or futakuchi-onna (a woman with an extra mouth in the back of her head).

Relevance to Inuyasha

Inuyasha deals with countless variety of yokai throughout the series from the more traditional such as Shippo (kitsune) and Hatchiemon (tanuki), to ones created by Takahashi herself, such as a dog yokai like Inuyasha or a mountain yokai such as Gakusanjin.