billion

number4

1. •
   the number 1,000,000,000, which is 1 followed by 9 zeros

   • At the last assessment it [the national debt] amounts to seven billion pounds (£7,000,000,000). — 1921
2. •
   Either of two large amounts.
3. •
   (old-fashioned) A million million (logic: 1,000,000²): a 1 followed by twelve zeros (10¹²); a thousand milliard.

   • n = 1,000,000,000,000, that is, = a billion, or the square of a million — 1778
4. •
   (informal) An unspecified very large number.

   • There were billions of people at the concert.