Locomotive numbers?

Okay, real newbie question. When I am looking at locomotives to buy they have a number after their name like 4-8-4 or 0-6-0. What do those numbers mean? I looked in some books and on the web but couldn’t find the answer anywhere.

Thanks

a 4-8-4 locomotive has four leading wheels arranged in a leading truck, eight coupled driving wheels and four trailing wheels in a trailing truck

The numbers refer to what is called the Whyte Classification System of Steam Locomotives. For a more in-depth look, check out this web site

http://www.steamlocomotive.com/misc/wheels.html

Dan