A contract between the allied forces and Austria stating the independence and neutrality of the latter. (while it literally means "contract between states" or "state-contract", as Zarkonnen correctly points out).
After the end of World War II, Austria and Germany were occupied by allied forces. Many people that had fled from Austria in 1938, when Nazi-Germany had marched in, returned, but a lot didn't.
The following period, from the end of the war 1945 till 1955 was a time of rebuilding and of economical reblossoming. From the beginning of the 1950ies on, politicans in Austria worked towards the end of the occupation. While american, british and french forces seemed rather willing to withdraw, the Soviets wanted to keep their occupation zone. In May 1955, a delegation of Austrian politicans flew to Moscow to have the Soviets sign the Staatsvertrag.
Many rumors and anectotes flourished about the negotiations leading to the withrawal of all allied forces till 26th of october 1955. The most popular one tells the tale of later chancellor Julius Raab and Karl Figl drinking with the Russians till 4 am, and cheating on them by secretly pouring away the vodka and having them sign when they where totally wasted.