A billion is a number with two distinct definitions:
American English adopted the short scale definition from the French.[3] The United Kingdom used the long scale billion until 1974, when the government officially switched to the short scale, but since the 1950s the short scale had already been increasingly used in technical writing and journalism; the long scale definition still enjoys some limited usage in the UK.[4]
Other countries use the word billion (or words cognate to it) to denote either the long scale or short scale billion.