Among many, many other interpretations and uses the one most interesting to me is as an
exclamation, though one whose precise meaning is difficult to pin down; when
shouted by practitioners of
Rinzai zen, its utterance indicates
satori or the attainment of
enlightenment, though claims are made that the
yell is used not only as an announcement but also as a tool by masters "to help students to overcome dualisms and ego-centric thoughts," no doubt in conjunction with slapstick-ly absurd violence and
koans.
It can apparently be employed in a broader sense as a "kiai"-style yell in martial arts.
Sometimes the Japanese yell is translated as khatz or kwatz; apparently the exclamation ho is used to similar effect in China.
"Katsu!" was reputedly the last word of 13th-century monk Hosshin, uttered as he completed his death poem:
Coming, all is clear, no doubt
about it. Going, all is clear,
without a doubt.
What, then, is all?