Pfand is the name of a currency that you receive at the supermarket, Biergarten or some outdoors parties when you buy some drink or food in some glass or hard plastic containers, or ceramic dishes, for example.
When you ask for your drink or food, you pay its price and also some more money, and in return they give you this coin.
The idea is that you give the container back when you finish and then you'll have the difference you paid before back.
In some places you won't have the coin and it's enough with presenting the container. Instead, in other places you must return this coin as a proof that you are the person who paid.
In the supermarkets you'll find some machines where you can introduce some bottles, tins and so on (they are marked with a logo, sentence or sometimes the cashier will tell it to you) and get the extra money you paid when you bought them. You don't need to wash them. The name of these machines is Pfandstation.
This system is done to encourage people to return containers and so they can re-use them later.
I hope I made myself clear and have a nice day :)