They've shared bills with AC/DC, Ozzy Osbourne and Judas Priest. They've produced rock radio staples with titles like Let's Get Rocked, Rock Rock (Till You Drop) and Rock Brigade. For 25 years they've kept their hair long and their heads banging.

But don't call Def Leppard heavy metal.

"We sit on the fence between hard rock and pop," Leppard guitarist Viv Campbell says of his band's role. "We can take 'hard rock,' but the heavy metal thing is an area we don't like to go into.

"It's a mantle we don't deserve. That's not what we're about. We do big pop songs with bombast -- and it's the bombast and the production thing that allude to being metal more than it really is."

And there you have it: Detailed analysis of the Def Leppard's music, from one of their own.

Of course, it's not that simple, as Campbell admits. Twenty-five years ago when Def Leppard emerged on the scene with the album On Through the Night, the debt to metallic contemporaries like AC/DC was audible. Campbell credits shared influences like Sweet, T Rex and Thin Lizzy.

"But there was a very clear point -- it was actually 1983 when Def Leppard released Hysteria -- when it went away from being just a hard rock or heavy metal influenced band," Campbell continues. "The songs were much better crafted and the production was 100% unique.

"By the time Hysteria came out that sound had absolutely been refined into being pop. There are a lot of guitars going on there, but it's not anything like a Judas Priest or Iron Maiden record, with big slabs of guitar. There are very, very subtle, nuanced guitar things going on and very production savvy subtleties all over Leppard's records. And stacks of vocals. Def Leppard is about three-part harmonies in the chorus."

Hysteria was the 1987 album that solidified Def Leppard's place in the rock pantheon, coming as it did on the heels of the massive Pyromania.

Call it glam, call it pop. Whatever the British band was doing, it was enough to convince a young Irish guitarist named Viv Campbell to catch them not once but twice on the Hysteria tour. Five years later, he would join the band, following the death of original Leppard guitarist Steve Clark.

"Joe (Elliott, vocalist) knew me and was championing me to join the band," Campbell, who had spent time with Whitesnake and Dio, recalls. "The other guys were a little bit skeptical because they only knew me through my reputation of being fired from every band I'd been in ... But it's been 13 years now. I've really got to work harder at being fired."

Should that happen, Campbell has a contingency plan in the works: A solo album of blues standards, due for release next month. Of course, he jokes, "it'll probably sell about 13 copies." So Leppard will go on.

As they have for a quarter century -- a remarkable feat even for a band built on bombast. Earlier this year, the band looked back at those years through a retrospective called Rock of Ages. Early next year, they'll add to the nostalgia by paying homage to some of their influences with an album of covers.

"Whether it's Coca-Cola or Def Leppard if you've been successful with a certain type of formula, you can only go away from that so far because that's what most people in want," Campbell acknowledges. "Def Leppard the band is known for big harmonies and choruses. And that's what we're meant to do."