To say that 'folk' is what can be performed at folk clubs is a circular argument. Nevertheless it is the reality. 'Folk' when used as a label for a genre can be no more than an imprecise idea, it is not a definition.

It's not so much a definition as an observation. It is pure Anthropological Empiricism. Go into a folk club and - this is what you're likely to hear. So the answer to the question what is Folk?' is simply the music that Folkies play. This includes Jim Eldon doing Dancing in the Dark, Raymond Greenoaken singing Sally Wheatly, Peter Bellamy doing You Can't Always Get What You Want (a regular encore back around 1988), Chas Sibbald singing Bat out of Hell and Phil Edwards singing Round Midnight.   One thing you might never hear at all is a bona-fide Tradition English Language Folk Song or Ballad. Or someone might tags one onto the end of a floor spot with an apologetic here's a Traditional One before launching into an approximation of June Tabor's macrame-beat version of While Gamekeepers Lie... which was aways more Victoria Wood than Bob Roberts anyway.

So - what is a Folkie?. Easy, it's someone who listens to Folk.   Cue theme to Ever Decreasing Circles.