Discover is a feature in the Google app, and on the Google.com mobile homepage. Google says this feature has grown significantly since launching in 2017 and now helps more than 800M monthly active users.
Publishers see more traffic from Discovery, as users explore new information by surfacing articles, videos, and other content on topics they care most about.
The data for Discover is being accumulated since March 5th.
According to Google, publishers that want to appear on Discover need to use high-quality images that are at least 1,200 px wide, and ensure that Google has the rights to display your high-quality images to users, either by using AMP or by filling out a form to express the interest in the opt-in program.