varies depending on where u are--generally in the uk a million has been regarded as a thousand thousands--1,000,000--so a billion was regarded in the uk as a million millions--1,000,000,000,000--in the usa, and in the computer age especially, a billion is regarded as 1 thousand million--1,000,000,000--in computer speak it is called a giga--a trillion would have been a billion billion in the uk but is now accepted as a thousand billion in the usa and in computers it is called a tera--the old million million and billion billion are not generally used now so when in the uk someone talks of a billion pounds it means 1000 million as in the usa and a trillion is 1000 billion--hope that helps--cheers