Today, February 11isisth is Banzai Day, in the Meiji era, citizens greeted the Emperor shouting "Banzai" as he headed to the ceremony to promulgate the Constitution of the Empire of Japan. This was the first time this greeting was held in Japan.
Literally "Banzai" translates as "ten thousand years" and means "long life to your imperial highness". Since the post-war period, Banzai has been an expression of joy and happiness. You could consider the traditional way of saying "Long!" (Super Tokyo Radio)