Here's a start:
CTR = Clickthrough Rate -clickthrough rate (CTR) is the number of clicks an ad unit receives divided by the number of times the ad unit is shown (impressions).
CPC = Cost Per Click - The CPC is the amount an advertiser pays each time a user clicks on his/her ad. Google AdWords has a CPC pricing system.
CPM = Cost per Thousand Impressions - The CPM is the amount an advertiser pays each time a user views his/her ad and an impression is recorded.
Impressions = The number of impressions is the number of times an ad is displayed on Google or on sites or products in Google's ad network.