BY JIM DEROGATIS POP MUSIC CRITIC

From the very beginning, "emo" (short for "emotional") seemed like a goofy name for a rock genre. The story holds that Washington, D.C.'s punk icon Ian MacKaye was onstage in the mid-'80s with Embrace (a short-lived group that fell between pioneering hardcore punks Minor Threat and the ongoing Fugazi) when someone shouted from the audience, "You guys are emo-core!"

"You mean like Emo Phillips?" Mac-Kaye supposedly responded.

Silly or not, the name stuck for a certain brand of heartfelt, hard-driving punk that is arguably one of the most galvanizing movements in the rock underground. It's also one of the most commercially vibrant, thanks to the recent success of Jimmy Eat World and several of the bands on the Vagrant Records label.

Every musician hates to be categorized, but in the case of emo, the pigeonholing is especially grating, since the term covers a wide variety of different sounds, from the "acoustic punk" of Dashboard Confessional, to the Midwestern rock of the Get Up Kids, to the artier fare of the Promise Ring.

"I would never go out there and say, 'I'm an emo singer!' " says Chris Carrabba, the driving force behind Boca Raton, Fla.'s Dashboard Confessional, which was on the bill Saturday at the Q101 Jamboree. "Personally, if I was going to label these bands myself, I wouldn't use that word. I don't see how you classify Sunny Day Real Estate, the Promise Ring, Saves the Day, the Get Up Kids, and Fugazi as one."

But Carrabba grants that the label can come in handy in one way.

"Genre labels can be useful in the sense that there's some dude in some Podunk town where there is no alternative to the rock station, and there is no underground scene, and there is no indie-rock record store, and no one else like him in that town, and instead of getting sucked into listening to country rock or the Backstreet Boys on MTV, once every couple of hours he gets to see this punk-rock stuff on MTV that's full of energy and he gets to feel the same thing I felt when I heard Green Day for the first time."

Matt Pryor, the leader of Kansas City's Get Up Kids, has a similar perspective.

"It's sort of like every year, a whole new group of people seems to learn the term, and so it just keeps coming back up again with different people," Pryor says. "We were called an emo band the day we formed, because the band I was in before was like a pop-punk band, and I was like, 'I'm not happy doing this; I want to do stuff that's a little bit more complicated.' Immediately all the pop-punk kids were like, 'A f------ emo band!'

"I'm used to it now, and it doesn't bother me at all, because I figure it's just sort of a marketing term," Pryor concludes. "It's sort of like the only people who really need to use it are journalists--no offense--and people who work in record stores."

But if you ask five different fans at an emo show to define the term, you're likely to get five different answers.

"What the heck is emo, anyway?" a fan named Andy Radin asks on the Web site of that name (www.fourfa.com). His answer: "Emo is a broad title that covers a lot of different styles of emotionally-charged punk rock."

Radin goes on to break the sound down into several subgenres: "emocore" (referring to mid-'80s innovators like Rites of Spring); "emo" (bands like Moss Icon and Indian Summer that followed in the late '80s and early '90s); "hardcore emo" (Heroin, Antioch Arrow, Mohinder), and "post-emo indie-rock" (Sunny Day Real Estate, the Promise Ring, Mineral, the Get Up Kids, Braid, Cap'n Jazz, Joan of Arc, Jets to Brazil).

All of this may be slicing and dicing things too finely for the general public, especially given that most young fans are only really acquainted with that last batch of bands, who record for popular indie labels such as Vagrant, Deep Elm, and Jade Tree. But despite their protests to the contrary, there are some sonic similarities among the best of these groups.

Emo bands tend to share a fondness for the dramatic use of loud/soft dynamics, complicated (for punk rock) arrangements, and an intense, breathy singing style. At their best, their lyrics lean toward moving personal poetry. At their worst, they're like solipsistic scrawlings from a sophomore journal.

The fans also have some things in common. The crowds that gather for shows at the Fireside Bowl or the House of Blues (the two most frequent hosts for emo in Chicago) tend to be resolutely unfashionable in a sort of anti-fashion "Revenge of the Nerds" way. And they are generally smarter, more discerning, and more sensitive than fans of pop-punk (Blink-182 or Sum 41) or nu-metal (Limp Bizkit or Linkin Park).

"I think emo is a reaction to the past few years of two things: the really saccharine, sweet, pappy pop music, or the rape-rock, college-meathead Limp Bizkits and Kid Rocks of the world," says Vagrant Records publicist Jessie Tappis. "There's an entire group of kids who were left out of popular music because of those movements, and they obviously had to go searching for something, because nothing being played on MTV or the radio was anything they could understand or relate to."

Yet much like the Seattle "grunge" scene of the early '90s, the only bands rushing to embrace the name "emo" are the ones that aren't really worth listening to.

"There is a tremendous amount of really terrible bands that have no problem calling themselves emo," says J. Robbins, a sought-after producer in the genre. But his own group, Burning Airlines, and most of the bands that he's worked with would just as soon avoid any label.

"The minute musicians are ready to put themselves in with this weird genre, there's trouble," Robbins says. "I love the idea that no one can say exactly why our stuff is quote-unquote 'good.' I love the idea that someone can say, 'Why is it good? Because I like it! It works.' That's all I really want--to be effective and affecting."

In the end, then, emo may be defined as much by what it isn't as by what it is.

"People call it emo because people need to call everything something," Tappis says. "But it's just rock 'n' roll."