What are the numbers in the name of a train?

[Phlegmak]

I'll make up an example:
0-2-0 Firefly

What the hell is the 0-2-0?

I've read it before, but I can't find it again. It would seem something so fundamental to the game would be mentioned in an easily accessible place in the manual.

(I'm referring to Railroad Tycoon 2, since that's the only one I've played, but I know that those numbers are used in the other Sid railroad games.)

 

[Charlie Babbage]

Numbers(sometimes letters) refer to driving and carrying wheels or axles. There are different systems used by different countries.

http://en.wikipedia.org/wiki/Wheel_arrangement

http://www.railway-technical.com/st-clasif.shtml