A "raver" is one who goes to raves. Contrary to popular belief, there are many different types of ravers.
First there are Candy Ravers; these are the ones you see running around shouting things like "PLUR!" or "Want a hug/sucker/glowstick/massage?" They are identifiable by their brightly colored clothing (phat pants being a must...if they're made of fun fur, all the better), enough Candy (brightly colored bead bracelets)to sink the Titanic, oodles of children's toys, as well as a few glowsticks and pacifiers. Candy kids are known as the cutest/most annoying people you will ever meet. A lot of them are pretty fake - it's impossible to be that happy all the time. Candy Kids are also notorious for being users of the drug Ecstasy - this is not entirely accurate, but with the way they dress and act, its not hard to see why this is assumed.
Next we have the "Goth" ravers. They're quite easy to spot - they will be dressed in all black, preferably incorperating some fishnet, spikes, and buckles into their outfits. The more there are the better. They will not socialize outside of the group they came with, and they will NEVER under any circumstances dance. They're too goth for that - dancing equates to happiness and celebration, and that's just not cool.
Ginos and Ginas (also known as "hoochies"). These are those well-dressed, snooty people that really shouldn't even be at a rave. The only reason they're at the party is to pick up on some 15 year old e-tard. Well, maybe not, but they certainly are only at the party to get a piece of ass. They will be dressed in whatever is "trendy" and do not know how to dance.
Next are junglists. Junglists are often viewed as being "agro". They listen primarily to Jungle/DnB music, and are partial to camo, hoodies, and clothing in dark colors. Popular junglist hairstyles are dreads (m+f), short hair (m+f), or short with two long bits in the front (f). Quite a few junglists are ex-candy ravers. They may also be "old-skool" or "jaded".
Old-skool and jaded pretty much fall into the same category. Old-skoolers are ravers who have been in the scene since "way back in the day". No matter how good the party is, the music/DJs/parties/drugs/people/anything else about the scene was WAY better when they first started raving. A jaded raver is not nessicarily old skool, but shares the same views as the old skooler.
And even still there are many ravers that do not fall into any of these categories. So...perhaps a raver is simply one who goes to parties to dance the night away, and loves the music. Interesting concept, hey?
And we all thought it was about the drugs. *sarcasm*
Rave is no longer a dirty 4-letter word. It's okay to be a raver. :)