While not as common as the banner ad, the skyscraper is another prevalent form of Web advertising. Skyscraper ads, which are tall and narrow, get their name from the tall buildings you often see in big cities. They are typically placed to the left or right of the main content on the page, which allows all or part of the ad to be visible even as the user scrolls down the window.
Skyscraper ads come in two standard sizes -- 120 pixels wide by 600 pixels high (120x600) and 160 pixels wide by 600 pixels high (160x600). They can contain text advertisements, images, or animations. When users click on a skyscraper ad, they are redirected to the advertiser's website.