What is N Scale
N Scale is a 1/160th scale replica of a prototype (real) train, building, person, automobile, and so forth. An N Scale locomotive is 1/160th the length, 1/160th the height and 1/160th the width of the prototype locomotive, and every feature (horn, bell air tanks, etc.) is dimensionally proportional (as close as realistically possible) to the scale of 1:160.
For reference, an N Scale 50' Box Car is approximately 3-3/4" in length and approximately 1 inch tall from the wheels to the roof. One N Scale mile is approximately 33 feet.
Originating in Europe, today N Scale is the second most popular modeling scale in North America (HO Scale is first) with about 22% of all modelers. A major advantage of N Scale is the small amount of space needed to build a railroad. It takes half the space required to build an equivalent HO layout. Conversely you can have twice as much layout in the equivalent HO space.
N Scale is sometimes referred to as "N Gauge". The term "gauge" when used correctly actually refers to the distance between the rails of the track. Prototype standard gauge is 4' 8-1/2". Track gauge in N Scale is 9mm. Hence the term "N" (Nine) Scale.