It's a loaded word. It means something, but the meaning has gotten twisted over the decades, for the profit of some, and to the irritation of others. You might see a "jazz musician" in a television commercial, maybe a twentysomething black man, well-groomed, in nice clothes, invariably playing a saxophone; whatever the product is, this is some attempt to imbue it with "sophistication", or some sort of "mature", no-green-hair hipness. You might see, in some other commercial, an older jazzman, black, of course, in nice clothes that invoke an earlier era of hip. A fedora or pork-pie hat speaks a thousand Madison Avenue words.

So that's jazz. Jazz is hip and sophisticated. You need read no further.

Actually, that's just a lie used to sell you stuff (including CDs). Jazz is neither hip nor sophisticated; it's just music. There are traits that vary from era to era, but there is a commonality to those traits that transcends the epochs.

There's improvisation at the center of it all. First and foremost, improvisation refers to the spontaneous creation of melody, and of its rhythm. Traditionally, that creation was buttressed by a framework - a song, with its preset melody and chords. An improvisor soloes, i.e. creates a new melody based on those chords; singers became part of the mix, thanks a great deal to Louis Armstrong, who evolved a vocal translation of his trumpet style, influencing singers like Billie Holiday and Bing Crosby, and just about any other jazz singer since.

But even the background was improvised. The remaining musicians often had only the melody and chords to fall back on, just the basics one would find on a minimally-scored piece of sheet music, so there was no indication of, say, how exactly the drummer should keep the 4/4 time, or what exact notes the pianist should play to voice the E Major chord. In early jazz, you also had horns improvising melodies in support of the lead (or soloist) horn, a concept of collective improvisation brought back over the decades in various forms, like the contrapuntal duets of Gerry Mulligan and Chet Baker, and, in its most enduring form, the all-out each-in-one's-own-musical-plane simultaneity of free jazz, often far removed from the song form and blues roots of earlier forms, but still containing the ineffable essence of jazz.

But if it's just about improvisation, that means Merle Haggard (from the tradition of "country jazz", i.e. the Western Swing of Bob Wills and the Texas Playboys) and Eric Clapton (improvisational roots in the blues, without which there would be no jazz) are jazz musicians too, right? Maybe so. That's part of the problem: if there is no "jazz police", patrolling the streets with eternal vigilance, then everything can ultimately call itself jazz.

Jazz harmony, for most of the 20th Century, has been based on seventh chords: a root note, with three other notes, successively a third higher than the previous one. The "seventh" comes from the fact that that last note is a seventh away from the root. The flavor of the chord comes mainly from the quality of the underlying triad - major, minor, diminished, or augmented. So Steely Dan is a jazz band, and so are The Beatles, since such chords occur in many of their songs. And both bands featured a little improvisation as well.

But none of these aforementioned examples (from Merle to Lennon & McCartney) are jazz. Something is missing, and it's not melanin. But what is it? Jazz might be best described as the set of jealously-guarded canons that have endured over the decades, even musics that divided one set of jazz police from another, once upon a time. Big band jazz, the orchestras of the likes of Fletcher Henderson, Paul Whiteman, Duke Ellington, and many others, introduced detailed, written-out arrangements of instrumental parts, but it still included improvisation, and was, musically, thoroughly in the then-young jazz tradition. The big rift came in the 1940's, with the advent of bebop, a loose, small-group form of the music, not really all that far-removed, in retrospect, from swing-era jazz. But the added harmonic and melodic complexity, plus the change from making-music-to-dance-to to an art for art's sake aesthetic, alienated much of the jazz audience of the day.

Bop would become the mainstream, i.e. the center of gravity of the collection of canons, and would evolve over the decades into its own little subgenres, like cool jazz, hard bop, and such. The mainstream of today would include swing-era stuff, and bebop in all its forms - the NPR version of "what jazz is". The more adventurous would include the 80s/90s mainstream: music derived from Miles Davis' pre-fusion groups, music championed by the likes of the latter-day alumni of Art Blakey's Jazz Messengers, such as Wynton Marsalis. And, yes, they all wear nice clothes, something especially important for the marketing of "Young Lions" like Joshua Redman.

But since the 1950's, jazz musicians have been extending the tradition in ways that alienated critics and audiences, akin to the days of the boppers; pianist Lennie Tristano had even tried free improvisation as early as the 1940's. Cecil Taylor began to find a way to fuse his love of Ellington and Thelonious Monk with the Prokofiev and Stravinsky and Henry Cowell of his conservatory training, and to improvise from structures completely removed from the preset chords and melodies of jazz tunes. This came to be known as free jazz, which, in turn, developed its own amorphous, overlapping set of subgenres over the decades, like free improvisation, "energy music", or freebop, for instance. Via the aforementioned Miles influence, some of this music has made its way, in somewhat manicured (and often subtle) form, into the mainstream, while the wilder or more non-conformist aspects remain as underground as they were in 1961. Those who sit in hope of the canonization of the avant-to-the-max Frank Wright or Sunny Murray will wait in vain, but many musicians, over the years, have become elder statesmen of the avant-garde, like the members of the Art Ensemble of Chicago, Taylor, Peter Kowald, and Peter Brotzmann, among many others. Some have received subsidies, such as MacArthur Foundation Grants, or have found careers in the academic world. But you will probably never hear them on NPR, nor see their latest CD hyped by retailers and portals.

The most commercially popular form of jazz over the years is Not Jazz, that is, watered-down jazz-like musics that are user-friendly enough to be hyped by the retailers and portals of the day. Often the music is made by real jazz musicians, which gives it even more of a veneer of validity, from the saccharine balladry of Harry James, to soul jazz, to the trendy R&B instrumentals of Ramsey Lewis, to the smooth jazz and the it's-jazz-by-virtue-of-sampling-old-jazz records of today. While indie labels have pretty much always been the media midwife of real jazz, large labels, aggressively marketing a combination of Not Jazz and conservative jazz vocalists, have usually been able to define, by sheer brute force, "what jazz is", much as Intel and Microsoft define all that is "computing" for a large number of people. Not Jazz is a varied tradition in its own right, and is often the centerpiece of "jazz" festivals worldwide.

Which is why the word tends to be a bit off-putting. If someone intones the word "jazz" (especially if it's preceded by an adjective like "cool"), I get the same sort of queasy feeling in the pit of my stomach that I would if a telemarketer were calling. Someone is trying to sell me something that I, a casual/hardcore jazz fan since childhood, wouldn't touch with a ten-foot pole, or it's a product, musical or not, being sold by invoking the idea of "jazz". Miles Davis, once the embodiment of the hip, well-dressed jazzman, abandoned the word sometime around 1965, for various reasons, including not wanting to be lumped in with the swirling commercial ghetto of musics called, rightly or wrongly, "jazz", especially in the face of the commercial ascendence of Beatles-era rock.

Other terms have sprung up since then. The musics Miles made after abandoning the word came to be known as fusion, and "smooth jazz" has its roots both in soul jazz and the more dumbed-down aspects of fusion; someone coined the word "fuzak" back in the 70's, in the wake of major labels like Warner (now part of AOL Time Warner) and CBS Records (now owned by Sony) flooding the market with slickly-recorded Not Jazz (also known, very briefly, as "Triple Z" jazz). Those two record labels, either for fear of alienating jazz fans, or fear of scaring away pop buyers, even had ads that extolled the new products of their jazz divisions, but deliberately failed to mention the word "jazz".

Others, irreparably divorced from the marketers' definition of jazz, would come up with new names: "creative music", "creative improvised music", "music in the (jazz) tradition", or the AACM's notion of "Great Black Music", part of the Art Ensemble of Chicago's motto, tying together the Dogon, the field holler, Charlie Parker, and James Brown, et al. These terms were mainly meant to invoke the connection between free jazz and the jazz musics that came before; fancier than the term "free jazz" - a relevant quote from saxophonist Chico Freeman: "Free jazz" means I don't get paid, a quip with multiple truths to it, from an era when loft jazz musicians were not yet welcome in large numbers. (The same applies to the "free music" of Germany's FMP). Dr. Billy Taylor, a mainstream pianist and educator whose career goes back to the late swing era, promoted jazz as "America's Classical Music", a uniquely home-grown musical artform that had grown as high-falutin' as anything in Carnegie Hall, and, now, the advent of such latter-day institutions as Jazz at Lincoln Center is a testament to the high-falutin' mindshare that the mainstream has won over the past quarter-century.

But, at the end of the day, it's just music. And "jazz" is still a loaded word, always ripe for more loading.