I always understood avant-garde to mean 'advanced guard' i.e. those forging the way forward in a direction which the mass of us would ultimately follow. Sort of like those tank crews who punch holes in the enemy lines and cause havoc and a breakdown of enemy morale, thereby allowing the infantry to sweep through more easily later on.
So in this sense 'avant-garde' has generally been a marketing or publicity label. Listen to this - it's the future, it's ahead of the game. No-one knows what direction the future of any music will taken - suggesting that X, Y or Z are the people who have anticipated the future is partially wish-fulfilment; and partially a desire to justify a liking for the wierd (or a liking for being seen to like the wierd) by claiming it as the future.
Interestingly much that was 'avant-garde' in 60s jazz, although it has had followers and created a rich tributary of its own, has otherwise been marginally followed and supported; its influence on the broad area of jazz seems to have been as just one of many influences - a colouristic device rather than the raison d'etre of the new musical age.
Which would...using my definition above...leave a question as to whether, looked at historically, it really was 'avant garde' at all. More an interesting and distinctive side-step.
I'd also suggest it makes the Coltrane of 1960-65 far more 'avant-garde' than the Coltrane of 1966-7.
Unless, of course, you take the view that these people (the 60s avant-garde) were so avant-garde that we still havn't got it and that at some point in the future jazz will shape up like Ayler or the Art Ensemble.
Rudd's point is well taken - his music seems far too diverse to be imprisoned by a label like 'avant-garde'.
[No comment on the quality of that music intended - some I like, some leaves me cold.]