Interestingly (or not, as the case may be), my dictionary defines "fiddle" (n) as "a violin, especially when used to play folk music; extended (colloq.) to any violin; extended to similar instruments such as bass fiddle..."

Which pretty much sums up what I thought - 'fiddle' is used colloquially as a generic term for any member of the bowed instrument family (violin, viola, cello, double bass). I've heard classical musicians use the term informally when discussing their instruments, but I guess this would probably be frowned upon by the classical music authorities, whoever they are ;-)

So, going by the definition above, maybe fiddle music is folk music played on a fiddle? Now all we have to do is define folk music... :-O

I fail to see what the presence or absence of sixteenth notes has to do with it though - don't they occur in both folk and classical music (and probably other kinds too)?