I agree that there are differences between Folk Clubs and sessions/singarounds

Folk clubs tend to look to having regular guests with a good standard of "floor singer" and tend to charge "club members"

sessions/singarounds tend to be unpaid flexible yet arranged meetings of like minded people

and then there are Concert venues where paid guests are paid to "entertain" whatever the definition is! and are not always called Folk Clubs ~ that's enough for one day!
Ray