An expandable ad is a type of online advertising format that allows an ad to expand or change in size or shape in response to user interaction. Expandable ads are often used to display additional information, such as images, videos, or text, or to provide additional functionality, such as the ability to sign up for a newsletter or download an app. Expandable ads are typically implemented through the use of JavaScript or other web technologies, and are triggered by user actions such as hovering over the ad, clicking on it, or scrolling past it. Expandable ads can be effective at capturing the attention of users and engaging them with additional content or features, but they can also be intrusive or annoying if not implemented carefully.