In common hobby usage "tinplate" is the term describing any toy trains which are neither to scale, nor even necessarily in proportion in their dimensions, such as classic Lionel, Flyer, or Marx trains. The term was derived from the fact that most pre-WWII toy trains were made out of stamped tin. At the same time it also applies to a hobbyist whose layout is modeled along the lines of a nostalgic and caricaturish toy train layout like those from back in the 1950's.
Hi-rail traditionally concerns more the particular way, or degree of seriousness with which the hobbyist employs his tinplate toy trains, modeling with them as if they were truly to scale. His layout's track, structures and scenery are all to scale in appearance just as is the situation with an HO layout. Thus, Hi-rail is the use of tinplate trains (classic Lionel, or Flyer) on an otherwise scale layout, one where all toy train items are absent and the layout is operated as a true model railroad, not as a child's train set.
The proper use of these terminologies has become increasingly blurred in the past dozen, or so years, with the introduction of high-end Lionel and MTH O-gauge models which were rendered to perfect O-scale (likewise other companies in S-scale) yet designed to still run on three rail track. Therefore, it now matters largely what modeling style/degree of realism the hobbyist employs on his layout, be it toy-like, or true to scale, in conjunction with his Lionel or Flyer trains as to whether the he is a tinplater, or a hi-railer.
NYW&B
