O scale (or O gauge) are model railroads in the scale range of 1:43 to 1:48. This scale was introduced by the German manufacturer Maerklin around 1900.
Toy trains have a third rail for current pickup. These toy trains (for example Lionel, MTH – or Maerklin in former times…) are often called „O-Gauge“ or „high rail“ in the US.
But O-scale also means 2-rail „scale“ railroads – and this site is about „O-scale“! Running on 32 mm gauge rails and built to 1:48 scale (in the US) and 1:43.5 or 1:45 (in Europe) O-scale model trains are double the size of H0 (=“half O“) and even 2 axle locos can have excellent current pickup in this scale because of the higher weight of the equipment.
Besides the standard gauge there are also narrow gauge railroads in O-scale:
0n3 = 3foot narrow gauge – (railroads like D&RGW used this gauge) and 0e = 750mm narrow gauge and 0m = 1m narrow gauge – with mostly European prototypes (like the RhB in Switzerland).