I learned about these the other day.
die Visitenkarte - Business Card
I know what Business cards are. A lot of people have them now a days. I didn't know where they came from. I never really thought about it before.
Apparently back in the day, when someone came to visit someone, they handed one of the servant their 'Visiting Card'. The servant then brought it to whoever the guy wants to visit. That person reads the card to see who is there and then decides to visit with them, more or less. Wikipedia has a nice explanation.
It is cool that in German they still call them Visiting cards even though they no longer have the same function as they once did. By keeping the name Visitenkarte, the history of their use has been preserved in most Germans' pop culture knowledge.