In September 2016 Microsoft introduced the Windows Defender Application Guard for the Microsoft Edge browser.
It is intended for the Windows 10 Enterprise version and will protect you while surfing.
It seems that this new function is already integrated in the Edge browser of the Windows 10 15031 and can be viewed as a preview.
Type about: application guard in the address bar, an info page opens up for this new feature. By Clicking on this message a short explanation will follow.
We’re determined to make Microsoft Edge the safest and most secure browser. Over the past two years, we have been continuously innovating, and we’re proud of the progress we’ve made. This quality of engineering is reflected by the reduction of CVEs when comparing Microsoft Edge with Internet Explorer over the past year.
Source: Microsoft – Blog.Windows