Microsoft has been holding the bug bash events for Windows Insiders for the last years, and rewards the participants with badges for their Insider accounts.
The last bug bash was held in November 2016, and Windows 10 insiders got a chance to bash those nasty bugs that were present in Windows 10 PC and Mobile builds. Quests were set up, to try some new and existing features, and point out bugs or improvements required if any. Now, the insider team has been, rolling out the badge of participation to the Windows Insiders, who were dedicated to being insiders and helped Microsoft in finding bugs in Windows 10.
The badges are still rolling out, so it could take some time before it shows up in your Insider achievement page.