"Hot spot" isn't a technical term, so it can get used on a wide variety of skin issues.
"Moist pyoderma" is the one that's most common, and what GRFers usually mean when they say hot spot.
However, an acral lick granuloma, which is a raw spot on a limb caused by licking, is also called a hot spot sometimes. The only difference is that a lick granuloma is created and sustained by licking and isn't necessarily sustained by an infection (yet). A lick granuloma can become acute moist pyoderma pretty quickly, so we often just blur the terms and say "hot spot" any time we have a raw or infected patch of skin that needs attention.
In either case, the dog will tend to lick or scratch at the spot and make it worse, so whether it's a granuloma caused by licking or dermatitis caused primarily by an infection, keeping the dog from getting at it is a key part of healing. Also, since a granuloma is really prone to infection, it needs to be kept clean just like moist pyoderma.
It's important to figure out if you have a lick granuloma or straight up pyoderma, because a lick granuloma can be a behavioral problem that needs to be addressed differently as it heals. Lick granulomas are usually acral (on a limb) and there's a lot of licking involved. Pyoderma often shows up almost magically and faster than you'd think it could happen.