1. the number that is represented as a one followed by 12 zeros
e.g. in England they call a trillion a billion
Synonym: one million million1000000000000
2. the number that is represented as a one followed by 18 zeros
e.g. in England they call a quintillion a trillion
Synonym: one million million million
3. a very large indefinite number (usually hyperbole)
e.g. there were millions of flies