Sometime around the new millennium, musicians began to take the term jamband as an insult. While any stylistic definition is by nature restrictive, to its credit, the word "jamband" is also a powerful tag—a description loaded enough to draw a specific cross-section of any city's live music junkies. As the experience of going to a jazz club often overshadows the specific performer or performance, the act of attending a jamband show now serves as a springboard for any number of urban adventures. So it's not surprising that many of the same faces turned out to see both Perpetual Groove and Umphrey's McGee when these fresh-faced acts strolled into New York City. And, while both bands have established their own sound, style, and specific-draw within the improvisational community, these divergent acts are united because they are bona fide jambands, who have openly embraced the phrase's surprisingly elastic meaning.

If Umphrey's McGee has come to represent the modern jamband movement's eager energy, then the Chicago sextet's recent Irving Plaza performance is comforting reassurance that the genre has a healthy future ahead. Located a block north of New York's 14th street artistic divider, Irving Plaza has long served as a point of arrival—-the final victory before a band officially breaks free from the city's dimly lit club circuit. Over a decade since second-generation jambands like Phish, Widespread Panic, and Blues Traveler established a blueprint for jam-nation's success stepladder, Umphrey's McGee grew up within the defined parameters of the term "jamband." That said, the group's Irving Plaza victory contained all the asterisks and essential teases necessary to turn their Friday evening performance into a full evening event instead of simply a showcase for tight improvisational music. And, from huddles of ticketless fans weathering the cold outside to the staircase-length smoking lounge lines, this Umphrey's show seemed to embody the modern, jamband experience, rumor-mill and all.

Opening with "Prowler," Umphrey's McGee celebrated its first headlining spot at New York's Irving Plaza with a string of surprise guests and special covers. While New York denizens Mike Gordon and Warren Haynes were both no-shows (despite rumors), a parade of collaborators worked their way onstage throughout the group's two sets. Near the end of the group's first set, what looked to be Motley Crue's Nikki Sixx (really Chad from Emptybag Productions) replaced bassist Ryan Stasik for a cover of the Who's "Baba O'Riley," a number which nodded to the evening's large, sweeping feel. Moving uptown after his own gig at Webster Hall, Keller Williams added some mouth flugel during "40s Theme," while, later, OM Trio's Ilya Stemkovsky acted as a second percussionist during a set closing version of "JaJunk." (OM Trio played its final gig a night earlier at the Tribeca Rock Club.) Nodding to his hometown of Chicago, actor Jeremy Piven also joined the group on percussion for a run through "Party Peeps" a few songs into Umphrey's second set. In another context, Piven's appearance may have seemed like a fluffy novelty, but in the context of this packed performance, the movie star cemented the group's celebrity credentials. Though it took the group a few songs to wet their feet, and overcome sound problems on "Dump City," Umphrey's rebounded with a choice segue between "Women Wine and Song," "Blue Echo," and "Jimmy Stewart." A tongue-in-cheek act with a cartoonish edge, Umphrey's early mishaps had an endearing, Revenge of the Nerds feel, making the group's late show highlights that much more victorious.

Umphrey's are an intriguing band to watch blossom because, not to long ago, the group's members were themselves fans working their way around the jamband junket. Thus, Umphrey's understand the inner workings of their crowd. Commenting on the stream of fans pouring out of Irving Plaza's overcrowded smoking lounge, Brendan Bayliss inserted the line "Everyone's outside smoking," near the start of the second set, a three-dimensional rendering of the evening's non-musical experience for those listening to this show for the first time on tape. And, in certain ways, it's these subtle phrases that have spawned a dialect of their own — easily understood by likeminded folks residing around the country.

Likewise, Perpetual Groove's performance at Tribeca drew a curious cross-section of New York jam-regulars. Like the Allmans and the Dead, Phish and Panic, and moe. and String Cheese, Perpetual Groove and Umphrey's McGee have unintentionally fostered a road warrior relationship: jambands hailing from different regions often leapfrogging along the club circuit and marquee space on festival bills. Conquering one market at a time, Perpetual Groove has avoided a full-on invasion of the Manhattan market, instead opting for gigs on the outskirts of the tri-state area. The perfect jamband, Perpetual Groove weaves a hodgepodge of styles and sounds into a slightly manic statement. Dipping into rock, jazz, funk, and trance, Pgroove are well-polished synthesists, able to tie such divergent genres together through the bright, euphoric solos of Brock Butler.

A hard Tuesday night bill, Pgroove's rare downtown show at Tribeca, planted the seeds for a successful future amongst budding New York jamband aficionados. Yet, unfortunately, the evening's intimate crowd deflated the club's energy and, in turn, stunted the group's mojo. A hard market to crack, especially during the stress of the pre-holiday season, New York can be kind or cruel to out-of-town bands. Around this time last year, Umphrey's played to a small crowd at BB King's Blues club, falling victim to weather and general weekday lethargies. Yet, Perpetual Groove performed with an abundance of energy, playing a fully stocked set, tied together by a series of choice segues. Opening with "Sundog," Pgroove jumped into full gear with "Stealy Man," a number that weaved gentle guitar lines into a bouncy, bass-heavy trance.

Oddly enough, while both Umphrey's McGee and Perpetual Groove have come to symbolize the jamband genre, both groups veer away from the term's patented free-flowing approach. Fitting snugly amongst a sect of artist's tied directly to Frank Zappa's jazz-theatrics, Umphrey's McGee are a composition-based band, using moments of improv to tie together charted sections and quick time-signatures. Showcasing the Sean Kelly-esque vocals of lead singer Brock, Pgroove also understand the importance of songcraft and lyrical development. A throwback to the more hook-oriented jambands of the early 1990s before groove began to outweigh composition, both Umphrey's McGee and Perpetual Groove sound like jambands even when they aren’t necessarily improvising. And, such a compliment is also proof that the term jamband now symbolizes an established genre.