A free app of mine just hit the app store, supported by iAds. I checked the profit details for iAds, and it says I've made a little money (few bucks). It also has data for a bunch of things, eCPM, Requests, Impressions, Fill Rate, iAd Fill Rate, and CTR. What do these mean? I can see that "requests" probably means simply how many adds have shown up, but I can't seem to make sense of the others.