The Auction House is a newly added feature to Diablo III. This allows players to put items up for auction, bid and buyout. The auction house uses Blizzard Credit, which can be purchased with real money; so far, rumors have it that 1 Blizzard credit equals one US Dollar. This may change for the EU servers so that instead of 1 Dollar it will be 1 Euro. You may also bid using in-game coin in a different auction house, but with the same idea.