Versailles is a city in France. It is the préfecture (capital) of the Yvelines département.
Versailles used to be an unimportant village a few miles west of Paris until May 6, 1682 when King Louis XIV moved his court to the Palace of Versailles there. Versailles is now a very bourgeois suburb of Paris.
The 1919 Treaty of Versailles ended World War I and established the League of Nations. Some other famous treaties were signed there as well, e.g. the Prussian King Wilhelm was proclaimed Kaiser of Germany on January 18, 1871 in the very same room, the "Hall of mirrors" (Galerie des Glaces, Spiegelsaal).
Other places named Versailles: