As the name suggests, snow boots are for precisely that – snow. If you live in a particularly snowy area or are going on a ski holiday and need footwear for getting around, these are what you should buy.
A snow boot is waterproof, or water-resistant at the very least. In most cases, a snow boot has a high side, keeping snow from entering the boot, and a rubber sole, to keep water out. Snow boots can be used in other wet conditions, not just snow, including slushy, muddy, and rainy situations.
They should extend up part of your leg, at least above your ankle, to keep snow off your feet and they are often heavily insulated for warmth. They make walking in snow or on ice much easier as well as being suitable for walking through streams.