A generally accepted definition of a Model Engineer is that it is someone who designs and or builds working scale models of engines or equipment. Most often the models made by Model Engineers are WORKING scale models, not static, display only models. However, almost all Model Engineers make a fair number of static models.
Most models produced by Model Engineers are based on real life engines and machinery. A model of a steam engine or internal combution engine will actually operate just as the original full sized engine operated. A tremendous amount of planning and work goes into getting these models to look and operate just as the real ones do.
Model Engineering usually involves the craft of Home Machining. Normally metal is the primary material used in making a model, but we use whatever material best fits the situation. This requires the acquisition of various types of metal and wood working tools and developing the skills to use them at a high level of precision.
Model Engineers build a wide range of models, in a variety of styles. One method is the art of scratch building. Here you start with a raw piece of material and cut and carve a part out of it. Another approach is to build from a casting kit purchased from a supplier or another modeler. Then there is the process where the Model Engineer develops patterns, makes castings from the patterns and finally machines the castings to create the finished model.
Model Engineers often develop their own designs. These designs are usually based on established principles, but include modification and ideas developed by the modeler. Model Engineering magazines are filled with articles showing designs developed by modelers.