In the case of armor I guess than these were the designs than Vic made to make a difference between light tanks, medium tanks (armor), heavy tanks and super heavy tanks. In the case with infantry, maybe its to difference between infantry, RPG equipped infantry, Jetpack Infantry and Robotic Infantry.
Amateurs talk about strategy. Professionals talk about logistics!
I'm not sure. Perhaps "Heaviness"? I know that some games represent things like Heavy or Super-Heavy tanks by taking the normal counter for Armour and shading in part of it grey or black.
You can look at your Raise Formations so see what's what that you have researched so far. Infantry with the bottom triangle shaded are MG or Siege. Two shaded triangles, the inf3, are Assault and Storm. That's all I've researched so far in my current game.