Kiai (気合)

Kiai (気合) (pronounced "key-eye") is a compound of ki (気) or Qi, meaning energy or life-force, and au (合), meaning harmony. In Japanese martial arts it commonly refers to a sharp shout made during the execution of a technique. Most kata feature several points where such a kiai shout is performed simultaneously with the technique. There are no specifically designated sounds, though Japanese dojos generally use single, elongated syllables beginning with a vowel. .

Although sometimes described as a kind of “battle cry,” kiai in daily Japanese also refers more widely to "fighting spirit," "giving one's all," "getting psyched up" and other such states of motivation, determination and commitment, in any field, not just martial arts or competitive sports. 

Kiai can be used to focus energy, startle an opponent, and even intimidate. The physical aspects of a kiai are often thought to teach a student proper breathing technique when executing an attack.  Correctly executed, that is to say by simultaneously and rapidly contracting the abdominal and other core muscles, kiai can also protect the lower body, shield internal organs, and provide solid abdominal support for striking techniques. Mental imagery is used to teach the practitioner to imagine starting a kiai in the tanden; as with breathing, it should start in the diaphragm, not the throat.

Donn Draeger, in his 1973 book on Classical Budo wrote:

“A well-made kiai produces a characteristic sound that makes the ears ring: it seems to come from a source deep within the trainee, and not merely to be caused by the vibration of his vocal cords. The tonal fidelity of the kiai is much like the unforgettable, deep-seated rumble of a lion at bay. The kiai indicates the degree of integration of mind and body in the execution of a technique. It is an unfailing source of information for the master, who thereby knows the trainee’s level of achievement.”