合 : Ai (put together, unite, combine, etc.)
When you use strong kiai at the moment of "kime" it makes your techniques more powerful and quicker. Also it is good to cheer yourself up and show your encouragement during the training.
There are many ways of shouting, typical kiai is e.g. "Ei", "Ya", "Hai", "Sei (for kyokushin karate)"... etc. Basically anything is ok but never shout "Kiai".. this is just funny. Let's refer to senior people and use proper ones.
