In the recent economic troubles, we’ve grown used to hearing about millions, billions and even trillions of dollars, pounds, euros etc. It’s worth noting, however, that these words do not have a universally-agreed meaning. What one person means by billion can be very, very different from that assumed by another.
A thousand is always 1,000 and a million is always 1,000,000. After that things become less clear.
In the USA, the name given to 1,000,000,000 is a billion. However, in Britain and other places, this figure is sometimes referred to as “one thousand million” with a billion being 1000 times more : 1,000,000,000,000. The following table lists the meanings of the various words in the “American” and traditional “British” systems :
“American” 1 billion
“British” 1 thousand million
“American” 1 trillion
“British” 1 billion
“American: 1 quadrillion
“British 1 thousand billion
“American” 1 quintillion
“British” 1 trillion
And so forth. In fact, the “American” and “British” labels are misleading. As the OED notes, both systems were invented by the French. And both have their merits. The “American” system has the advantage of convenience. It’s easier to say “one billion” than “one thousand million”. On the other hand, etymologically, there is something to be said for the “British” system. A billion is the second power of a million (a million times a million), a trillion is the third power and so forth. This fits in with the bi- and tri- prefixes.
In Britain, people use both systems and this can and does cause confusion. It’s fair to say, however, that the “American” system is being used more and more and the “British” system less and less. The UK government has been using the “American” standard since the 1970s. On the whole, the “American” approach is probably the better one to take as it’s what most people will understand. But it may be worth spelling out exactly what you mean by these terms if you find yourself needing to use them.