RE:RE:43 MILLIONS IMPRESSIONS OF AN EXTREMELY OBSCURE METRIC
If an ad is shown for 1 second you have an impression. If you have 4 ads on a page that change every 10 seconds, then after a minute, that user generates 24 impressions. If he refreshes the page there are four more. There are better metrics. One thing is for sure, a 100 impressions does not mean a 100 users.