Trading cards usually come in packages and often contain pictures and stats of athletes on sports teams. For example hockey, baseball, football etc... When you buy a package of say, 5 cards you don't know which ones you'll get until you open it because they are random. For this reason people often trade cards in order to acquire a full set i.e. every member of every team!
For example let's say I have 2 @papa-pepper cards and someone else has 2 @meeterboom's. We could trade. If a card is very rare we might have to trade 3 for one and so on!
It's huge in North America.
This is a huge producer of trading cards. http://www.upperdeck.com
Thank you very much for the explanation! I think in German it is called "Sammelkarten". It sounds more like "collect" than "trade". Othervise it would be called "Tauschkarten".
Steemit is gorgeous, because I learned today the topic "trading card".
Mille grazie, cane vecchio.