Where did the name AR15 origanaly come from, why is it called AR15?

from the maryland ar15 website:

"AR means ARmalite the company that first designed and produced the AR-10 (the AR-15s .308 big brother) before the AR-15.  Armalite made a variety of firearms including shotguns (the AR-17) and bolt action rifles (AR-1 and AR-5); all with the AR designation (so no - it doesn't mean Automatic Rifle nor Armalite Rifle). Note that the Armalite of today IS NOT the Armalite that developed the AR-15.  The orginal Armalite was a division of Fairchild Aircraft.  The name 'Armalite' was purchase by Eagle Arms several years ago and is used to produce their premium line of AR-15 and AR-10 rifles."