Question on enemy "types"

[TK (Shad)]

Weapons mods state more damage to different enemies types such as "Boss enemies, powerful enemies, rank-and-file enemies," What... indicates what an enemy is? Boss is pretty clear in MOST cases... but what about the others? What designates an enemy as "powerful" vs "rank-and-file" or "major"???? Especially in the legendary campaign? I am asking so I can maximize my weapons performance.

[ZeBunisher]

red healthbar = rank and file
yellow = major

[Jagdtiger]

Rank and file enemies are any enemies with red healthbars, and a couple of times this phrase is used it also includes orange healthbar enemies.
Powerful enemies are orange, yellow, and boss health bar enemies (usually means anything but red).
Major enemies have yellow health bars that appear above their head.
Bosses (Also known as ultras) are enemies with a yellow health bar that appears at the bottom of the screen