A milliard is the European term for what wimpy Americans call a billion, that is, one thousand million, or 10 to the 9th power. In recent years, the British have also adopted the American terminology, rendering the term milliard essentially obsolete in English. (It still appears in French and German).
The divergence becomes self-perpetuating. In English, 10**9 is a billion, 10**12 is a trillion, and 10**15 is a quadrillion. In the European system you need 10**12 to be called a billion, and 10**18 to be considered a trillion. And the word for that intermediate case of 10**15? You've guessed it, that number is called a billiard.