An interstitial ad is a type of advertising format that is commonly used on the web and in mobile apps. An interstitial ad is a full-screen ad that is displayed between two pieces of content, such as between two web pages or between two screens in an app. Interstitial ads are often used to display rich media or video ads, and are designed to capture the user's attention and engage them with the ad content. Interstitial ads can be effective for advertisers, as they can provide a large and prominent area for displaying ads, and can be easily integrated into the user experience of a website or app. However, interstitial ads can also be intrusive and disruptive, and can potentially annoy or frustrate users if they are not displayed in a user-friendly manner.