SS, what you're describing is a philosophy, not a definition. You're celebrating that ordinary people are coming together to make music. I agree, that's worth celebrating. However, according to you, when people get together to make music, of whatever origin, that's folk. It's a point of view, but I don't think it's one that many would share, and neither does it reflect everyday language or experience.

There are recognisable genres of music, although they many not be easy to define, and playing them out of their usual context doesn't alter that. A jazz piece is still jazz, whether it's played in a folk club or a jazz club, just as Bach is still Bach, or hip-hop is still hip-hop, wherever it's played. Similarly, a folk song is still a folk song whether it's played in a jazz club or a classical concert hall. You cannot define "folk", or anything else, simply by its context.

The "folk club" is not as unique or special as we like to think. Everywhere, amateur musicians are coming together to make music, in choirs, orchestras, jazz clubs, and countless other venues. They're all sharing the same experience of making music. To label what they're doing as "folk" because it's done by folk is actually quite patronising.

What you are really saying is that you have something which calls itself a "folk club" at which all and any kinds of music are welcome. That's great. I won't even argue with you over whether it should be called a "folk club". But to call everything that is played there, or which might be played there, "folk music" doesn't help us towards a definition of "folk" in its modern usage, which is what I had understood to be your question. The club could be called something quite different, the music would remain the same.

Why not just say that at your "folk club" people are encouraged to perform not only traditional and modern folk songs but any other genre as well? Why does it all have to be forced into the label "folk"?