I have no idea what these are
Digital trading cards that Steam randomly attaches to your account for playing associated games. If you get a full set of one game’s cards, you can combine them into a badge you can put on your profile. Then I think you can upgrade your badge by doing it again.
not just badges but also steam backgrounds and emoticons ;3 … also foil cards… on games you dont really like, you can sell the cards… it is something that steam users mostly like, collecting and trading the cards :) . And as ‘useless’ as it is, some users dont buy games unless the games have steam trading cards!
edited by rosedragon on 3/12/2015