"banner" ads

The phrase web banner is often used to refer to a form of advertising on the World Wide Web delivered by an ad server. It is also known as a banner ad. It is not to be confused with a non-advertising banner at the top of a web page that graphically identifies the website it is on or this website's prime content, which type of banner is technically known as the hero image.

As a form of online advertising, the web banner, or banner ad, entails embedding an advertisement into a web page. It is intended to attract traffic to a website by linking to the website of the advertiser. In many cases, banners are delivered by a central ad server. When the advertiser scans their logfiles and detects that a web user has visited the advertiser's site from the content site by clicking on the banner ad, the advertiser sends the content provider some small amount of money (usually around five to ten US cents). This payback system is often how the content provider is able to pay for the Internet access to supply the content in the first place. Usually though, advertisers use ad networks to serve their advertisements, resulting in a revshare system and higher quality ad placement.

Web banners function the same way as traditional advertisements are intended to function: notifying consumers of the product or service and presenting reasons why the consumer should choose the product in question, a fact first documented on HotWired in 1996 by researchers Rex Briggs and Nigel Hollis. Web banners differ in that the results for advertisement campaigns may be monitored real-time and may be targeted to the viewer's interests. Behavior is often tracked through the use of a click tag. Many web surfers regard these advertisements as annoying because they distract from a web page's actual content or waste bandwidth. In some cases, web banners cover screen content that the user wishes to see. Newer web browsers often include software "adblocker" options to disable pop-ups or block images from selected websites. Another way of avoiding banners is to use a proxy server that blocks them, such as Privoxy. Web browsers may also have extensions available that block banners, for example Adblock Plus for Mozilla Firefox, or AdThwart for Google Chrome and ie7pro for Internet Explorer.

...
Wikipedia