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

Hit — 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 views (see next item) is a much better way to measure traffic.

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

CPM — Cost per thousand impressions. A way to price banner ads. If an advertiser's CPM is $25 then you get 1000 impressions of your banner on his/her site for $25.

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).