My understanding (which may be wrong, so correct it if it is):
FRS (Family Radio Service) doesn't require any license. This is the frequency range that the standard-issue cheap(ish) walkie-talkies (like Talkabouts) all used, exclusively, until a few years ago. On your walkie-talkie, it's channels 1 through 14. Regulations limit the power you can use to half of a watt. This gets what's usually described (for marketing purposes, anyway) as a 2-mile radius, though that really only applies if the other side of your conversation is in sight of you.
GMRS (General Mobile Radio Service) requires an easy-to-get license that costs money, but doesn't require any tests or training. This is the frequency range that's now on the newer cheap(ish) walkie-talkies. It's the channels above 14 (usually - some brands may number the channels differently). Regulations allow higher power in this range (5 watts, I think), which yields the "5-mile" marketing radius. I believe that the newer walkie-talkies do, in fact, adjust their power, so they transmit with .5 watts when you're using an FRS channel (<= 14) and 5 watts when you're using a GMRS channel (> 14). It seems likely that a lot of people who buy walkie-talkies never bother to get a GMRS license. I doubt anybody will ever track them down, particularly at ski areas.
There's also CB (Citizen's Band), which was, of course, a big fad many years ago. It's also low power and doesn't require a license. Because it's much lower frequency than FRS and GMRS, it can get a longer range if used with a big antenna ... not that you're likely to go skiing around with a 10-foot antenna sticking out of the top of your head.
A whole variety of other frequency bands are out there, which are used for all sorts of things. Some of these are used for two-way voice communications, but allow higher power and have much longer ranges, so they're much more regulated -- there are real rules about how you're supposed to use them, they require more expensive licenses, getting the license requires you to show you know the rules, and in some cases getting the license requires you to show you're going to use it for its intended purpose. It would be a really bad idea, I think, to start using aviation radios (e.g.) around the ski area..