Glue-Down
vinyls are thinner vinyl tiles or planks that are adhered directly to the subfloor using full-spread adhesive.  

Floating
is a method of installation where the Vinyl Floors are not adhered using glue. They can be click-lock or loose lay products.

Underlayment called "pad," is a moisture and sound barrier that goes under the Luxury Vinyl Plank flooring. Look for labels that say "attached pad," and you won't need to buy this separately. If you love a Vinyl floor that does not have the pad attached, it also comes on rolls that can be placed separately before the flooring is installed. 

Wear Layer this is the protective coating on the surface of the vinyl planks. They are measured in "mils" and each mil is equal to one layer of saran wrap.  6 mils + is rated for residential use, 20m+ is commercial quality.The thickness of the wear layer determines how long the flooring will look new.