1,000,000,000 is the natural number following 999,999,999 and preceding 1,000,000,001. With a number, "billion" can be abbreviated as b, bil or bn.
In standard form, it is written as 1 × 10⁹. The metric prefix giga indicates 1,000,000,000 times the base unit. Its symbol is G.
One billion years may be called an eon in astronomy or geology.
Previously in British English, the word "billion" referred exclusively to a million millions.