A piece of code inserted into an ad slot in order to display an ad.
There are different types of ad tags, including HTML or IMG, JavaScript, iframe, and SafeFrame ad tags for display and mobile, as well as VAST (video ad-serving template) and VPAID (video player ad interface definition) ad tags for video.
The goal of an ad tag is to request certain information and carry out processes when the web page or mobile app loads.
The term tag also refers to non-ad tags, such as those used for web analytics.