It's a term to "weigh", (pun intended), the options available in O gauge to create a model RR that is representative of the real world. Even though most trains produced are 1/48, the track is 1/43 due to the spacing, so true scale is not possible unless track and train are modified or hand laid and custom built. Do what we like, and we can be happy. Perfection is unattainable, so close counts.
Don