Definition-Defying Display

Ask the experts — be they documentarian Ken Burns or Wikipedia — "What is jazz?" and you may come away confounded. No one can quite say. Even the word's etymology is fuzzy, pertaining perhaps to "pep," to baseball, or to the scent of jasmine so prevalent in N'awlins brothels. Such a fog of uncertainty becomes jazz, in that it is the most mutable of musical forms. It could encompass big-band orchestration (see Duke Ellington), small chamber ensembles (Modern Jazz Quartet), or even act like a rock band ('70s-era Miles). Jazz emulates and celebrates a true sense of democracy through group improvisation, where all voices can be heard.

In its 13th year, and after nearly facing cancellation, North Beach Jazz Festival kicks off yet another five days of festivities this week. "This is not your father's jazz festival," founder Alistair Monroe boasts on the fest's Web site. It's no idle claim, in that the form has embraced so many variegated strains of music that all genres seem to become meaningless. Dominant in 2007's proceedings are turntablists, funkateers, reggae bands, and ensembles emphasizing their Latin roots. Thursday night trucks in Aluna Colombia, Austin-based group Maneja Beto, and a group led by Salvador Santana, son of Carlos.

Friday night, subtitled "Jazz Forward," highlights music that incorporates jazz approaches in spontaneous music creation to varying ends. Dutch DJs Kraak & Smaak will be lugging crates full of acid jazz and trip-hop beats while native son DJ Zeph will pit his turntables against a live band.

Those looking for a purer strain of the art form will want to catch the meeting between Hammond B3 master Reuben Wilson (a longtime recording artist on Blue Note in the '60s), Grant Green Jr. (son of the string-bending great), and drum legend Bernard Purdie on Saturday night. Purdie has scored porn soundtracks and played behind everyone from Hall & Oates to Steely Dan, no doubt understanding that it's all jazz, whatever that means.