Scale
Scale refers to the proportional representations of people and objects in relation to the real-world or, more frequently, to the size of a person.
In the LEGO community scale is most often referred to using some variant of the term x-wide where x is equal to whole number representing the number of studs. This shorthand is commonly understood and provides a guide for builders.
Scales in the LEGO world
Consistency of scale has never been a hallmark of the company nor of the greater community.
Other Train Scales
Trains are built in many scales which is a source of great debate in the world of trainheads. As noted above L-Gauge sets are primarily 6-wide but many in the train community believe that true minifig scale trains should be 7 or 8-wide.
One odd note for those familiar with model railroads, there was a time when LEGO produced HO scale automobiles as accessories for sale within and, as additions to, town sets [1].