9 x 19

Nowadays, we normally refer to the cartridge as "nine millimeter," short for the 9mm x 19mm standard also commonly referred to as 9mm Luger, the "Luger" coming from George Luger's name - the guy who invented that famous and iconic German pistol.

But every once in awhile you hear people call it "9mm Parabellum". That comes from George Luger's employer, Deutsche Waffen und Munitionsfabriken, and their company motto: Si vis pacem, para bellum. That old Latin phrase means "If you want peace, prepare for war."