Here's a breakdown of the basic White's boots, starting with the Smoke Jumper and trying to provide reference points:
Smoke Jumper - The standard boot for firefighting, adapted to many other uses. Has a soft bellows tongue and a large lug sole that is both stitched and screwed on. Can be made in any height starting at 6" and can be lined or unlined.
Farmer/Rancher - Identical to the Smoke Jumper, save for a flat composition sole or mini-lug.
Classic Work Boot - A farmer/rancher with a 90 degree block heel and the C641 last which features an upturned toe.
Bounty Hunter - Identical to the Smoke Jumper, save for being built on the lower profile last of the semi-dress. Typically comes with a flat composition or mini-lug sole, but one could be built with the large lug.
Packer - A farmer/rancher with a western last and heel.
Semi-Dress - A 5" height boot with a lower profile last. As far as I have seen (I do not own any) it does not use a bellows tongue and comes with flat laces.
Retro Semi-Dress / Americana - It's not exactly clear how they make these distinct from the standard semi-dress, but often they feature a 90 degree block heel.
Hopefully that clears up some of the issues people have with White's admittedly esoteric distinctions.