The number 1,000,000,000.
The company is worth a billion dollars.
Billions of stars are in the galaxy.
In American English, a billion is 1,000,000,000. Spanish billón usually means 1,000,000,000,000, so use mil millones for this word.
Common phrases & grammar
a billion dollars · a billion people · billions of dollars · one billion years
a billion + noun
billions of + plural noun