What is SCALE?
A scale model is a virtually EXACT replica of the original, usually reduced proportionally to a different size.  The "scale" is a dimensional ratio where one foot of the original is reduced some number of "scale feet" for the model.  As an example, 1:48 scale means an object 48 feet long would be one foot long as a model.  The scale model is dimensionally correct in length, height, and width.  Its parts are  proportional to the scale.  The model is usually finished to appear as the original appeared.  For model railroading there are several scales, each identified alphabetically for ease of reference.  The most common model railroading scales are: 

With scale modeling there is some reasonable deviation in size to accommodate function.  An obvious example is couplers, which are generally oversized to ensure functionality.  Couplers are defined by a standard and are accepted throughout the model railroading community, including The Great Scale Model Train Shows.


What is Non-Scale?
Non-scale models are generally categorized as toys.  The model may or may not be a copy of a real object.  If  a model of a real object is out of proportion and/or varies from its true configuration it is a toy, and not a scale model.  The most obvious examples of toy trains are oversize wheels and track, or engines and rolling stock that are severely out of proportion.  

Are all scales seen at the Scale Shows?
The Great Scale Model Train Show includes all of the popular model railroad scales.  These are the scales that have an associated railroad scale letter, such as Z, N, HO, etc.  So you will see 1:220, 1:160, 1:87, etc.