A Banner Ad is a rectangular graphic display on the side edges of a display.
Ad servers deliver those banner ads to a certain application or website. If a banner ad is displayed, the user can click on this banner and is then taken to the App Store or a corresponding landing page. Since the format of banner ads is largely accepted, advertisers can easily place their advertisements in apps or on websites and publishers can accept ads from most advertisers.
Banner Ads are usually paid through cost per impression, cost per click or cost per action and mostly aim to promote a brand or to activate or reactivate users. They are image-based rather that text-based and are the most popular form of website advertising.
Banner Ads have been the most popular form of mobile advertising for the last years but seem to drop in popularity as Native and Video Ads become more popular.