No harm meant to FB users, BTW. It's just not for me.
:-))

Somebody mentioned "Sing Song" earlier.

That's quite a good term but, arguably, too all encompassing to describe a gathering for "our kind of music" whether traditional or more contemporary.

In my younger days, "sing songs" were quite common particularly in some of the pubs and clubs where older people gathered. Even on the last bus home.

However, the participants weren't usually folkies and you might hear anything from current hits to old standards including Sinatra, Bing crosby, old music hall songs, musical songs, even hymns!
If there was the occasional folk song, it wouldn't be thought of such or even occur to people there that it might be one.

Of course, that was before the days of background music, juke boxes, TVs etc in pubs when people just liked to relax. There wasn't even fruit machines, pool tables etc back then although you might get darts and dominoes in public bars.
You also had these old lovely "snugs" and nooks and crannies in pubs which you no longer see as the tendency is to knock everything into one big barn or use the lounge as a restaurant.

So these days, people are far less likely to to want to sing or play music of any description just for enjoyment and when it happens, it usually needs to be "organised" or "advertised" in some way.

There are usually expectations about what is or isn't welcome or acceptable in a session whether this is strictly enforced or not and people make choices accordingly. That's not necessarily a bad thing, of course. At least, not always.