Thanks for your question. I actually should have explained that in my article as well ;)
The reward pool is a virtual pool that contains all STEEM available to be distributed as rewards. To put it short, the more STEEM in the pool, the higher the rewards.
Do please edit your post with this added info. Thank you.
OHHHHHH that makes sense !
and its no worries, your article was excellent, it was just something i was wondering about, thank you very much for the reply :)