Kiai  is a Japanese term that is a compound of ki  meaning mind, will, turn-of-mind or spirit and ai being the contraction of the verb awasu, signifying "to unite"; literally "concentrated spirit". In martial arts, the term refers to a short yell that some martial artists shout before or during a fight or technique. Korean martial arts may call this sound a Yatz or Kihap. In bujutsu (Japanese arts of war), it is usually linked to the inner amassing of energy released in a single explosive focus of will.

Kiai is used for:

* a psychological effect on your enemy.
* a psychological effect on yourself, so-called "amping yourself up".
* to provide an escape route for exhalation of air.
* to keep air pressure in your body balanced (holding your breath while taking impact – from a kick, punch or the ground – can cause injury).
* to rapidly contract the transverse abdominals and other core muscles to provide support for striking techniques and protection to the internal organs