This one's for Gary S.

[nachoman]

The "Whyte" system refers to classification based upon the arrangement of pilot wheels, driving wheels, and trailing wheels:

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Thus, a locomotive would be a 2-8-0, 4-4-0, 2-8-8-2, etc. The first number is the number of pilot wheels, and the last is the number of trailing wheels. Both pilot and trailing wheels are non-powered. The middle number(s) refer to the number of wheels driven by the cylinders. If there are two sets of cylinders (as in an articulated locomotive), there are two sets of numbers corresponding to the number of drive wheels driven by each cylinder.

The names are just what railroads called each wheel arrangement under the Whyte system. It is much easier to say "ten wheeler" in a conversation instead of "four-six-zero". Different railroads often used their own names, and political conflicts also resulted in different names. 2-8-2 was "Mikado" in the USA until Pearl Harbor, and then the PC crowd came in and thought it wasn't right to have a Japanese name - so they were renamed "MacArthur" after the general. After the war "Mikado" came back into usage, and is still the most popular name for that wheel arrangement.