In English, a “billion” is 1 000 000 000 (a thousand million). If we wanted to refer to a thousand million, we simply said “thousand million” or more rarely “milliard”. ... But in 1974 we officially adopted the US practice of using “billion” to mean a thousand million.

Is billion and milliard the same?

A "milliard" was what we now call a "billion," or a thousand million. What they called a "billion" was a 1 with 12 zeros after it (which we call a "trillion").

When did a milliard become a billion?

The British Billion was 1,000,000,000,000 until circa 1974 when American astronomers decided to de-value it to 100,000,000,000 as they said it was easier to calculate light years. Then someone adopted 1,000,000,000 as the new billion.