Billion is a word for a large number, and it has two distinct definitions:
American English adopted the short scale definition from the French (it enjoyed usage in France at the time, alongside the long-scale definition). 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. Moreover even in 1941, Churchill remarked "For all practical financial purposes a billion represents one thousand millions...".
Other countries use the word billion (or words cognate to it) to denote either the long scale or short scale billion. (For details, see Long and short scales § Current usage.)
Milliard, another term for one thousand million, is extremely rare in English, but words similar to it are very common in other European languages. For example, Afrikaans, Bulgarian, Catalan, Czech, Danish, Dutch, Finnish, French, Georgian, German, Hebrew (Asia), Hungarian, Italian, Kazakh, Kyrgyz, Kurdish, Lithuanian, Luxembourgish, Macedonian, Norwegian, Persian, Polish, Portuguese (although the expression mil milhões — a thousand million — is far more common), Romanian, Russian, Serbo-Croatian, Slovak, Slovene, Spanish (although the expression mil millones — a thousand million — is far more common), Swedish, Tajik, Turkish, Ukrainian and Uzbek — use milliard, or a related word, for the short scale billion, and billion (or a related word) for the long scale billion. Thus for these languages billion is a thousand times as large as the modern English billion.