MRAID, or "Mobile Rich Media Ad Interface Definitions", is an industry standard API for rich media ads running in mobile apps. Using the MRAID API with HTML5 and JavaScript, rich media developers can communicate between ads and apps, and access certain device functions.
Learn more about MRAID from the IAB.
Google's GMA (Google Mobile Ads) SDK supports the MRAID standard up to version 3. Creatives that run on mobile app display inventory, including banners and interstitials, can use MRAID JavaScript according to the specifications.
In addition, Google supports the IAB's Open Measurement SDK.
Respond to bid requests with MRAID creatives
You can bid on any request with an MRAID creative as long as the bid request does not specifically exclude the MRAID creative attribute MraidType: MRAID. In OpenRTB, we send the Banner.api signal, where APIs 3, 5, and 6 correspond to MRAID 1, 2, and 3.
If an app publisher does not allow video interstitial ads (in other words, display-only interstitials), the SDK automatically adds a close button 
useCustomClose() is not supported. You can check whether an ad slot is a video-allowed interstitial based on whether the video message is included in the bid request.
To learn about best practices or how to specifically bid on interstitial ads, see the Real-Time Bidding Protocol and Bid Response Guide.
You can learn more or see detailed examples of SDK functionality in the Google Ad Manager Help Center.