Every unit has a tag in it's name on the battle map in square brackets, saying what classification it is.

They run something like:
Missile
Light Infantry
Heavy Infantry
Spearman
Missile Cavalry
Light Cavalry
Heavy Cavalry
Artillery

What do they mean? Are they based on some kind of calculation of the unit's stats, or are they just an assigned value? Is there some kind of property being one type and not another carries?

Sometimes I've compared the stats of one type of infantry deemed "Light" and another deemed "heavy" and there's not a lot in it, if anything at all.

Also what is the property of their weapon type being "Light" or "Heavy" based on? Again is it something that's just assigned, or based on the properties of the weapon they use?