Beginners to the wonderful world of model railroading often get confused with the term “prototype trains.” Generally, model train enthusiasts will refer to the real (full size) trains as prototypes. As the name implies, every train track system is a unique, one of a kind system.

This explains why the phrase ‘prototype train’ is a good description for full size trains.
If, as a model train set enthusiast, your aim is to create your own “real” system, then it’s easiest to refer to full size trains as being the prototypes.