Few kinds of music have a history as tortuous and complicated as jazz. Hardly surprising, since it's been around almost three times as long as its kid brother, rock 'n' roll...

IF YOU ASKED a handful of people "What is Jazz?", you'd get a handful of answers involving, probably, improvisation, Louis Armstrong, rhythm, saxophones, and the mysterious concept of "swing". There's so much confusion and misunderstanding that it's tempting to refer only to "jazz" in quotation marks. Just listen to a solo saxophone improvisation by Anthony Braxton or Evan Parker, followed by a Duke Ellington song from the '30s. Somewhere there's a connection, but it may not be immediately obvious.

In fact, the whole terminology is redundant. Lumping together over 80 years of musical development under the heading "jazz" is as inappropriate as labelling Pink Floyd, the Buzzcocks and Rick Astley as "pop". It may be accurate, but it's not in the least bit helpful.

Swing was the thing in the 1930s; a decade later Charlie Parker played bebop; and in the early '60s musicians and critics referred to "the new music". So perhaps a more useful reference point is a "jazz" tradition, and the evolution of the music.

In the beginning, slavery transplanted a nation of Africans to the New World of America. There they clung to their African social and musical traditions, even as the slave owners enforced western values on them through the church and the whip. Inevitably a new musical form came about, mixing western melodic and harmonic method with the rhythms and spirit of African traditions. The new musical form was to become "jazz".

At the turn of the century, a distinct piano-based style known as "ragtime" evolved. Its distinguishing mark was consistent syncopation (the stressing of the off-beat against an on-the-beat pulse) to a degree previously unheard of. Its most famous exponent was Scott Joplin.

Most of this new music was created in the southern United States, and New Orleans became a centre for its development, giving its name to an early style. Ragtime was adapted to group playing and improvisation (always important in African music, but largely ignored in the west since the days of Bach) became a crucial feature. Jelly Roll Morton was an early star, and Louis Armstrong achieved great success from the '20s onwards.

From the outset, "jazz" had a tarnished reputation in the eyes of the establishment. The very word "jazz" has its origins in sexual excitement, and the music was played in bars and brothels. Another significant factor acting against (and on) "jazz" was racism, which has yet to be eliminated. In the '20s, top soprano saxophonist and clarinettist Sidney Bechet settled in Paris, where he found acceptance as a musician rather than rejection as a black man.

Gradually, attention shifted north. Out of Washington DC came Duke Ellington, arguably the most famous "jazz" musician ever. Working with the two prevalent forms of his day - the blues and the standard A-A-B-A song form (ie. a repeated theme, a bridging chorus, then theme again) - Ellington opened up harmony and orchestration to an unheard of extent. Filling his band with outstanding instrumentalists and penning uniquely beautiful melodies, Duke influenced almost every contemporary musician - and still does today.

From the late '20s through to the start of the Second World War, swing and big bands ruled the roost. Fletcher Henderson, Count Basie and Ellington are the most important names, along with Benny Goodman and the brothers Dorsey. The '30s also saw the ascendance of the saxophone to an almost definitive role as the jazz instrument. Players like Coleman Hawkins and Lester Young were the stars of the show, and influenced the whole generation that followed.

By the start of the '40s, the big band era was drawing to a close. In New York small combos were now calling the tune, and experimentation at a club on 52nd Street evolved into a revolutionary new style, "bebop". Being new, people couldn't handle it and branded it "anti-jazz". But it survived and grew, with pianist Thelonious Monk, trumpeter Dizzie Gillespie, drummer Kenny Clark and saxophonist Charlie Parker leading the way. Bebop was exciting and fast, and extended the frontiers of harmonic and melodic improvisation. A simple seventh chord would have ninths, elevenths and thirteenths piled on top, fifths would get flattened, and substitute chords would be used as a basis for soloing. Rhythms became jerky and angular, and audiences began to listen more, rather than just dance.

In time, bebop also exhausted itself. Dizzie Gillespie combined bebop with Latin rhythms to produce an early fusion. White players, especially out on the west coast, began to make innovative contributions instead of just imitating and watering-down black developments. Then trumpeter Miles Davis introduced "cool music" as a reaction to the fiery themes and tempos of bebop, and popularised modal playing: instead of improvising along with chord changes (which at this stage were many), the soloist used a mode, or appropriate scale, which fitted the whole chord sequence.

As cool music was replaced by hard bop and post-bop, exemplified by Art Blakey and the Jazz Messengers, the groundwork for a revolution in "jazz" was being laid down. Bassist Charles Mingus had been around since the '40s, but in the late '50s his experiments with collective improvisation (ie. the whole band improvising, not just the soloist) opened new doors. Jelly Roll Morton had had his band improvising in the '20s, but only with standard song forms. Mingus and his colleagues opened it up for everyone to improvise, so a song structure could disappear to leave just music.

Just as important as Mingus, but not nearly so widely acknowledged, was (and is) "the mighty Sun Ra". Ra was playing synthesizers "as if they were invented for him" in the '50s, released literally hundreds of recordings, did pioneering work in all styles of "jazz", and influenced scores of top musicians philosophically as well as musically.

From 1957 onwards, the arrival of Ornette Coleman made earlier disputes between boppers, swingers and traditionalists seem like playground squabbles. His heresy was playing without chords, unified tonality, or a clearly stated beat. From the title of a seminal Coleman record, this became known as "free jazz" - free from restrictions of time or tonality. Not surprisingly, a lot of cacophony arose from this style of playing, and many an innocent ear rebelled against this new "anarchy".

Yet the work of Coleman's band and pianist Cecil Taylor set new precedents which were taken up by John Coltrane (after his modal phase), Archie Shepp, Pharoah Sanders and Albert Ayler - saxophonists all. Free musicians often associated themselves with civil rights and black militancy, rejecting the word jazz (because of its manipulation by a racist music industry) and referring to their work as "the new music". Black musicians' collectives were formed to promote the new music which was (and is) consistently ignored by the mainstream media and, consequently, the public. The Art Ensemble of Chicago were in the forefront of such moves - appearing on stage semi-naked with face paints and mountains of percussion to emphasise the African origins of their music.

From unlimited freedom there seemed no place to go - until Miles Davis started off a chain of fusions: indo-jazz, afro-jazz, jazz-funk, and from the '60s, the classical/jazz mixes of Cecil Taylor and the contemporary/jazz music of Anthony Braxton.

As we hurtle towards the '90s, the no-wave music pioneered in New York by James Blood Ulmer, Jamaaladeen Tacuma and Ronald Shannon Jackson fuses more elements: funk, rock and free jazz.

The names mentioned above are just a few signposts down the road of "jazz" evolution. These are the people with the biggest reputations and the most widely available catalogues of recordings, and many of them have made a great deal of money from playing "jazz".

It's just as well there's such feeling and love for the music, however, because if financial prospects were the sole consideration, it would have disappeared long ago. "Jazz" is not a clever way to earn a living anywhere, and Britain rates poorly for exposure and appreciation.

The commercial heyday of "jazz" ended in America with the advent of rock 'n' roll. This was promoted by the white American music industry to such an extent that "jazz", an essentially black form, didn't stand a chance. As rock 'n' roll marketing really took off, "jazz" musicians found it increasingly difficult to earn a living.

In Britain, "jazz" ceased to be popular music and became art. It is now heavily dependent on subsidy and grants for its survival. Some musicians feel bitter about this, considering it like being offered crutches when a cure for their lameness is possible. Others accept it as a fact of commercial life, and get what they can. Workshops and teaching support others, and many players feel happiest with the security of a "normal" job to subsidise their music-making.

So regardless of the relative success of Courtney Pine and the (now defunct) Guest Stars, "jazz" remains a marginal music. While all manner of worthy fads pass over the turntables of John Peel and Andy Kershaw, "jazz" is steadfastly ignored. Plagued by popular misconceptions, it is often perceived as difficult, self-indulgent, and cliquey. These charges contain elements of truth, but not necessarily in a negative sense.

It can be difficult to play and to listen to. But it's a case of "you gets what you puts in". The more effort you make, the bigger the rewards. Many "jazz" musicians are highly skilled on their instruments, but if you think it's self-indulgent to be technically capable and to strive to develop new sounds and directions, that's your problem. A tight-knit "jazz" scene does exist, which can seem cliquey and weird. But it's not: it's just a small community of people who share a love of the music and take it seriously.

With some limited media attention, the "jazz" scene in Britain is relatively healthy at the moment. The "Acid Jazz" movement, is just one of many strands of development that are proceeding at an electric pace.

But there are storm clouds on the horizon. It's possible, if not probable, that continued cuts in arts funding will hit "jazz" particularly hard. Failing a conscious decision by the music industry to promote "jazz" as popular music (which it could do, but won't), audiences will continue to be small and financial rewards minimal.

Still, this is nothing new. The artistic rewards of this resilient and creative music will ensure its survival. The small numbers who play it and listen to it have sufficient commitment to keep it going - and growing.