1, 000,000, 000,000, 000,000 or 10^18
...from tri as in three.
It is lazily commonly missused for a million millions, which is in fact a billion, from bi as in two (...and not a thousand million).
You see, a tricycle does not have two wheels and a bicycle does not have one and a half wheels.
2. Proper Noun, plural (Trillions/Trillion$): An underground rap group from the Dirty West.