It is a natural number used in Europe to represent one thousand million or milliard. In 1947 US practice was officially adopted which replaced the term milliard with billion, which mean a thousand million. Since that term milliard went out of US English but it is being used in some European languages such as French milliard, Spanish milliard, Polish milliard, and Russian milliard.
The term milliard only represents one thousand million which is equal to one US billion. In US practice, term billion is used while in some European languages, term milliard is used, and this is the only difference between US and British usage.