The Frost Festival 2018 Badge was a limited badge that was available only during the Frost Festival 2018 Seasonal Event. It was the first badge which instead of Xmas was called frost festival.
The badge was claimable by going to the 'Coupon Code' page, and entering the code: "FrostFestival2018" however it expired.
This badge belongs to a group of event badges, each of which could be unlocked on a particular holiday.