ctr: click-through rate, the percentage of impressions that results in a click through. for example if a banner was clicked on 87 times after being shown 1000 times, it would have a CTR or click-through rate of .087 or 8.7% (87/1000 = 0.087×100 = 8.7).
impression: a single display of an ad on a web page, mobile app, or other delivery medium. an impression does not have to be viewed or clicked on to count as an impression. see also billable impression, forecasted impression.
conversion rate: the percentage of visitors to a website/app who sign up for advertised offers or buy advertised products. proven high conversion ratios (via web analytics) add value to a website’s inventory.
inventory: this term refers to the amount of ad space available on a website. to calculate an accurate inventory figure the number of possible page impressions in a certain timeframe should be taken into account, as well as the number of zones available for ads to be shown per page.