i think that Kihon is basic practice of Martial Arts moves, such as punches, kicks or other strikes or blocks.
when i've trained Kihon for first time, with basic set of moves, it was painful, tiring process. moves were inefficient, slow.
then learned to execute them better, much better, even if not perfectly.
now with new set of moves, i go through the same ordeal... execution is laughable, whole body moves like a 'fat kid's ass', even if it's a punch from other guard position.
i call this training: '2nd Kihon'.