August 8, 2008
A "click" occurs when someone sees one of your ads, clicks on it, and is taken to your website. This is when you are charged by Google or Yahoo for Ad, on the search network.
What is an impression?
An "impression" occurs each time your ad is displayed. If you are advertising only on the search network, you will never be charged for an impression, only clicks. On the other hand, if your ad rarely gets a click, Google will cause your ad to go "inactive", meaning it will no longer show, and why should it?
What is a cost-per-click (CPC)?
A "cost per click" is the average cost paid for each click. CPC = Total Cost / Total Clicks