Even so, I have always wondered what the definitions are for hi rail, 3 rail scale, and is 2 rail hi rail or is it 2 rail scale?
I am sure others have their definitions/views on this, here is my shot at it:
Tinplate- that emphasizes the 'toy' nature of the trains, usually have layouts with tinplate track, with the accessories and such, that seeks to replicate the kind of experience kids had with their Christmas tree layouts or the old 4x8 with the artificial grass on it. The emphasis is not realism.
3 rail hi rail- The idea is to try and make the layout more realistic looking, hence they might use non tinplate track (or tinplate track made to look more real, with extra ties, painted, etc) that is ballasted, they will have structures that appear more realistic looking, weather things, have ground scenery, backdrops, and so forth. With hi rail, it isn't that strict, people can and do still run semi scale equipment, they may have operating accessories but try to blend them in more, they may try more realistic operational schemes and they want the overall look and feel not to be as 'toylike'.
3 rail scale- This is kind of like the 'big brother' of hi rail. People into 3 rail scale often will convert the couplers over to kadee to be more in line with scale, they will buy equipment that is only prototypically to scale (so for example, will run vision line or imperial line scale engines, but would not run Williams stuff that is mostly non scale), they make the track look as realistic as possible, want it to be as close as possible, do realistic looking scenery, and many design their layouts for operation in a protypical manner (and again, there is no one definition, these are just typical of what I have seen). It doesn't mean someone with a 3 rail scale layout migth not occassionally run old cherished semi scale stuff, just means their emphasis is on as much realism as possible.
2 rail- with 2 rail, I would argue by default it is 2 rail scale, while there is equipment in 2 rail that is semi scale (especially if people convert over 3 rail semi scale to be able to run on 2 rail O track), most of the people in 2 rail are in it to do the realism thing IME. There probably are variations in 2 rail as to how prototypical they want to be, whether they are to the rivet counter level or if they are okay with stuff not perfect, etc.