My son got a hold of a little teeny flashlight several months back.  It has a tiny elastic attached to it that allows you to put it on your finger.  He immediately named it a pogon (po-gone).  From then on, he keeps tabs on the pogon.  He finds it and plays with it non-stop for a few days and then it goes missing again and then it is re-discovered.  When he re-finds it or sees another version of it somewhere, he knowingly identifies it.  He earnestly states, "ah, there's the/a pogon". I like knowing what a pogon is.

What words have been invented by you or your kids?