CPM - Cost per Thousand of Impressions of ad banner ("Cost per Mile").
CPC - Cost per Click
CPC - Cost per Lead

Impression - A measure of how many times a banner is displayed. Count one impression each time the banner is shown.

Hit - Any successful file request. Hit is a questionable measure of web site traffic. Count one hit each time a browser request is made from a web server. For example, a page containing 5 images counts 6 hits each time it is viewed (once for each image and once for the page itself).

Page view - A measure of how many times a complete page is displayed. Count one page view each time a page is displayed.

CTR - Click-through ratio. A method of rating how many times a banner is clicked on. A ratio of the number of times a banner is shown to the number of times it is clicked on. For example, if a banner has a CTR of 20:1, it means that 1 out of 20 people have clicked on it (i.e. 5% of the people who viewed it).
ROI - Return Of Investments (in ad)