Trillion is a million million. One trillion is written 1,000,000,000,000. This definition is standard in the United States and is used throughout World Book. In some European countries and elsewhere, 1 trillion can mean 1 million times 1 million times 1 million, or 1,000,000,000,000,000,000. That number is equivalent to 1 quintillion in the United States. See also Decimal system (The decimal system and number words) .
