The Tripartite Pact was signed between Italy, Germany and Japan on 27 September 1940. It was an anti American alliance, stating that each country would aid any of the others that was attacked by the USA.
The significance was that it bound all 3 to fight against America if America entered WW2 on the side of Britain (the only country still fighting Germany and Italy at the time), or if USA attacked Japan; all 3 were expressing official hostility against America, a neutral nation at the time, and therefore the opposition of all 3 to any country that had a liberal democratic system of government.
However, following the Japanese attack on Pearl Harbor 7 December 1941 and the German and Italian declaration of war on USA 11 December 1941, the Tripartite Pact became entirely defunct, as all 3 signatories were now at war with America of their own choosing.
