Typically means they are over wound to increase output. Pickups are a basically a magnet(s) with wire windings. Hot pups sound good distorted, but are sometimes noisy and muddy sounding at clean settings imo.

Though that is a simple explaination, perhaps someone here more knowledgable than I am (would'nt take much), can explain it further.

Seymour Duncan website has a page where you can see the profile for each pickup it makes with a sound clip to give you an idea of what it will sound like. Very clever marketing imo. They sell lots of pups.