Google has developed One Tap, a new system that lets users sign up on sites and in apps with a single touch on devices users have logged into with a Google account. Developers will need to integrate this into their products so you can use it.
The idea is that not only users will be able to sign up quicker without having to fill out a form on Android, but they will also be prompted to sign back in with just a tap via the account you registered with.
Of course, users can already sign up for apps using your Google account and avoid filling a form, but this is designed to be even more streamlined. Since users are already logged in on their Android device, Google will just run with that instead of asking them to provide Google account password a second time within the third-party app.