An iframe is a type of HTML element that allows a website or app to embed content from another website or app within its own pages. An iframe is typically used to display external content, such as videos, maps, or forms, within a web page or app. Iframes are often used in advertising, as they allow advertisers to display their ads on a publisher's website or app, without the need for the advertiser to host the ad content themselves. This can make it easier for advertisers to deliver their ads to a wider audience, and can also make it easier for publishers to monetize their inventory. However, iframes can also raise security and privacy concerns, as they can allow external content to access and manipulate the website or app in which they are embedded.