what exactely is the ecpm?

[GiveMeMore]

I read it in google adsense help, but i didn't quite understand what it really means if you can help me know how to use it :(

thanks

[Lipik]

Earnings for every 1000 impressions.
So if your website brings you 30$ in one day with 7000 impressions, your ecpm is 30/7= 4.25$
This is a good indicater to check how you site is doing. It's better dan only look at you pageviews or only look at what a click brings you.