No matter how many twists and turns Umphrey's McGee takes into prog-rock, metal, trip-hop, and, occasionally, free jazz, the group will forever be saddled with the term "jam band." That's a dirty little label that makes most fans bristle, inviting all sorts of cliches. Can't a glassy-eyed college dude rock a Grateful Dead T-shirt and dread-locks in peace anymore?
Let's get this straight. Umphrey's McGee does like to jam, sometimes noodle, over languorous songs that build to a fever pitch and then suddenly disperse in a whole new direction. But the Chicago-based sextet is also fiercely committed to improvisation, and a live show, such as Thursday night's at the House of Blues, is truly the best microcosm of its music and the scene it inspires. (Yes, there were a lot of Dead T-shirts, and yes, at least five guys near me squatted on the floor to light a joint out of security's eyesight.)
Here's the thing about jam bands: You either love them or loathe them. One man's 10-minute odyssey full of spacebound solos is another's excuse for an extended bathroom break (and a third gin and tonic). But if you're willing to make the journey - and at the House of Blues, that meant three hours of music lasting until nearly 1 in the morning - Umphrey's McGee is happy to take you along.
The band, which formed in Indiana in 1997, ignites something transcendent in its fans, who relish the musical detours and relentless energy, but also the collective musicianship. Umphrey's likes to play off its members' chemistry. Guitarists Brendan Bayliss and Jake Cinninger, both exceptional musicians who were selective in their shredding, often stood locked in place as each man deciphered and then complemented what the other was doing.
Words often get in the way for Umphrey's McGee, and they often mistake platitudes for memorable songwriting. On "Ringo," their vision of utopia is decidedly simple: "And if your wish could be granted/ What would you say?/ To live in peace forever and a day."
It was easy to look past such throwaway lines, though, because the music took on so many shapes and sizes. What's two minutes of junk when the odyssey is 10 minutes long?
James Reed can be reached at jreed@globe.com. 
