What is this exactly? I clicked the ? but i didnt really understand it. I aksed because my current one is $266.22 which is waay higher than what it has previously been? I am a little confused..thanks.
eCPM is not very useful. It tells you that IF you received 1000 ad impressions (page views), AND you received the same CTR (not likely), AND you received the same pay-per-click (not likely), you would earn that much money. Since we probably don't get 1000 impressions per page, and CTR varies widely, and pay-per-click changes often thoughout the day, eCPM is not useful in helping us understand our Adsense performance. I do not understand why the figure is even shown. It's much more useful to look at CTR and actual earnings.
Effective CPM is a measure of your average earnings, per thousand clicks. You can increase your Effective CPM by selecting topics that attract high bids from Adsense advertisers, and building pages and whole websites on higher paying topics. Although Google doesn't release information on Adsense bids, you can get a good idea of the top paying topics by looking at information on Adwords bids, or, for that matter, bids on pay-per-click search engines like Overture. There are a number of keyword research tools available, both free and paid, that can help you find high paying topics.