An overlay is a type of ad that is served on top of a web page or app, and that covers a portion of the content on the page or app. Overlay ads are typically served in the form of display ads, or interstitial ads, and are designed to be viewable and engaging on a variety of devices and platforms. Overlay ads can be effective for advertisers who want to reach and engage users while they are consuming content on a website or app, and who want to deliver value and relevance to their target audience. Overlay ads can also be beneficial for publishers and platforms, as they can provide a new source of revenue and a more engaging user experience for their audience.