Ki, what is it?

"Ki" (body and mind coordination)
If the origins of nearly every traditional martial art in existence today were explored, one would find that the theories and principles of 'ki' training are in existence in the original teachings. Many martial artist today who are studying these arts do not understand exactly what 'ki' power really is. Although some people like to market 'ki' as some mystical power that only they possess, 'ki' is no secret. The word itself translates to "energy, life- force, spirit, and/or breath." It also represents the scientific phenomina of physics. It is also refered to by Christians as God's Holy Spirit which God breathed into Adam after forming him out of the earth (dirt). Everyone has 'ki': If you didn't, you'd be dead!

The above is from the following:

http://www.hapkiyoosool. com/ki.htm