Greetings!
I´ve so far only played horde but noticed something: Almost every rp guild which post their recruitment, speaks of “light RP” their offer. I´m not used to this term.
Are non light RP guilds any different? Do they exist at all?
The confused little orcling
This is simply a guess, but I guess it can be that guilds labeling themselves with “light rp” can use that as a reason not to have events regularly, having members that doesn’t rp and such, people who wants to do some rp from time to time but not really committing perhaps 
The labels have always been really dubious and vary from person to person. In general I’d personally say that “light RP” when compared to “heavy/hardcore RP” (or whatever other pseudo-elitist name we want to give it) means that in Light RP people talk IC and have some lighthearted events, but their characters don’t necessarily have the same depth or are demanded to have the same in-universe consistency.
So-called “heavy RPers” claim to give their characters a continuity, and in general they try to have them be an actual representation of a person fully living in the world (when they are IC). Light RPers might not be as concerned with this, and will just go IC for a bit of fun, without as many constraints. A lot of light RPers also don’t seem to be playing a character, but rather speak as themselves if they were in their characters’ body.
Ultimately it’s not set in stone, again, different people have different concepts of these things. But with a promise of light RP you can expect them to not be taking it as seriously. I’m trying to find a suitable metaphor that doesn’t sound patronizing, but you could say that many heavy RPers would see themselves as fully involved actors in a play or a movie, while many Light RPers might be akin to going to a renaissance faire one day for fun. You’re still taking part in acting in both cases, just with a different level of dedication.
I’d assume ‘light’ would be the frequency of which RP events occur (rarely in this case). It’s a term usually used by umbrella guilds trying to fill their roster with as many different types of player as possible.
As for RP focused guilds, there are a few on the Horde that I know of.
As someone recruiting for a “light RP” guild, pretty much what Richter said.
I actually didn’t know if it was a general term, I just tried to grab something to communicate that we’re more casual than more committed RP guilds, who might have mandatory RP events and expect you to have a fully worked out character backstory etc.
Can I please resurrect the 13-year-old jokes about heavy RP being for Tauren and Light RP for Gnomes?
Pretty please? 
~narrows eyes~ Are you saying that I am… fat?
Nooo! She’s just saying you could feed an ARMY my dear BEEFDancer!
~scribbles furiously~
Mhmmm… don’t mind me, just adding names to my kill list here.
Now, if you were so kind to type in /pvp…
Ohh come on now! Don’t have a COW over it… I mean all you need is to BEEF up your day!
Finding this amoosing, aren’t you? You better HOOF it, or you’ll be getting the horns when I stampede all over you!
<cackles like mad!>
Utterly hilarious this is yes!!
Maybe if you calf about it you will be able to bull your way.
I wonder… If you jump on a Taurens back and clings on… Do it count as a Rodeo??
Its something to Mooose about I think!