I will give these a try from my perspective:
Riding Lawn Mower: These would be the smallest riders available - usually a rear engine rider with a cut width a bit wider than most push mowers. Example: Snapper 301123BV
Garden Tractor: A larger heavier lawn tractor with enough horsepower to handle ground engaging implements like a rear tiller. Example: JD GT or GX series.
Lawn Tractor: A rider with the classic tractor form where the engine is in front and the operator sits in the rear. Usually has a hitch to be able to pull a trailer and tow behind implements like rollers, sweepers, etc. Example: JD L,LT or LX series.
Farm Tractor: A larger tractor with enough power to run most any smaller farm PTO implements like hay mowers, balers, etc. Minimum 40 HP in my opinion.
SubCUT: The smallest variantion of the CUT, barely bigger than the large garden tractors, but with more standard capability. Example: Kubota
BX23, JD2305.
Please note these definitions are my opinion and not any kind of official definition!
/forums/images/graemlins/grin.gif