A floating floor clicks together and rests on the slab without being attached to it. A glue-down floor is bonded to the slab with adhesive. Both are legitimate installs for luxury vinyl plank, and the right answer depends on the room, the product, and the slab.
Floating is faster, slightly cheaper, and more forgiving of minor slab imperfections. It needs expansion gaps at every wall and a transition strip every thirty feet or so, which can interrupt a large open-plan space. Heavy furniture and kitchen islands can also pin a floating floor and cause gapping elsewhere.
Glue-down is the stronger install for big open rooms, high-traffic areas, and anywhere a solid feel matters. It has no hollow sound, handles rolling loads, and stays put under islands and heavy furniture. It does require a flatter, cleaner, drier slab, so the prep is more involved: moisture testing, grinding high spots, filling low ones, and the right adhesive for the product.
Our rule of thumb: floating for bedrooms, offices, and smaller rooms where speed and cost matter; glue-down for great rooms, kitchens, and whole-house installs where the floor needs to feel like one solid surface. Either way, the slab gets tested and prepped first, because that's what makes a vinyl floor last.