Also see advertising terminology on the Internet.
In banner advertising on a Web site, the clickthrough rate (CTR) is the percentage of times that viewers of a Web page click on a given banner ad, causing a request for the advertiser's Web site to be transmitted to the viewer. For example, if two out of every 100 visitors to a Web page clicked on a given ad, that ad would be said to have a 2% clickthrough rate. (In most cases, a 2% clickthrough rate would be considered very successful, by the way. In many campaigns, especially as ads become familiar to users, the clickthrough rate is well below 1%.)
Many advertisers rate the success of a given ad placement on clickthrough rate alone. Other advertisers also place a value on the visitor's viewing of the ad, which is believed to create a desired company or product brand impression over time.