I wonder if there's a website somewhere where there are people arguing about "What is Jazz?", and a section of them hotly denying that Trad Jazz really counts as Jazz? On account of a presumption about how an essential element of Jazz is that innovation must always be in the driving seat, whereas, in Trad, innovation is a bit suspect. "That stuff isn't Jazz" they'd protest - "It's folk music."

With us it's the other way round - innovation is tolerated rather than idolised. (See this thread for example).

It seems to me that the situation is best represented by one of those Venn diagrams, with circles intersecting each other. Folk music, in all its varieties, is one circle, and Jazz, in all its varieties, is another circle, and where they overlap you find Trad Jazz.
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"What do you mean by Trad Jazz? 1920's-style?"

Yes - and pre 1920s.