You're probably more aware of WebView after the recent dust-up over security issues in older versions of Android. WebView is a tool developers can use to display web content in an app without implementing a whole browser, and today Google is opening a beta test for WebView on Android 5.0 and higher. Simply head over to the Google+ page to join and get the latest tweaks and fixes.
WebView was based on WebKit in Jelly Bean and earlier, which was the reason for the aforementioned dust-up. KitKat switched to Chromium, and Lollipop improved things further by separating WebView from the system so it can be updated via the Play Store as needed. This is where the beta channel comes in. You can sign up to be a beta tester and the latest builds of WebView will be pushed to your devices. This is only for Lollipop devices, though. KitKat and older can't update WebView independent of the system.
The first version in the beta channel will be based on Chrome 40, which was released in December. You might not notice a difference as a user, but developers will have an opportunity to test apps with the new version of WebView easily. If you want in, just join the Google+ group and opt into the test.