Someone, in a reply above which I can't find now, said

"for example you wouldnt see Bob Lewis or Dick Miles OR RonTaylor ,booked at Dartford folk club.,neither would you have seen WizzJones at Nottingham Traditional music club.
so why waste time on definitions,we can decide from looking at a guest list."

YES BUT......

I'm a folk dancer who goes to an occassional concert. I know what I like (Martin Carthy, Jim MaGeen, CHARM). But I don't know any of the names above. So the guest list is no help to me.
Definitions like "traditional" mean that I know what sort of thing I'm getting.
Not that I don't enjoy some recently written songs, but I wouldn't want to spend time at whole concert of them.

So back to my warhorse. People should be given as much information as possible (especially on Folk Festival Programmes). Those who are 'in the know' will know anyway. Those who don't know the kind of songs WLD sings or the kind of dance Hilary Herbert calls (challenging ones usually) need that information. I took my daughter and friend to Whitby this year and they found half of the programme unintelligible -"what is Playford, is it a concert, a dance or what?"