and..
I grew up understanding that a 'jam session' was when the musicians fed off each other and the next song/tune would be started by whoever started it..it might be somebody beside you, might be someone across the clump.

What do you all call the kind where everybody plays together but the play goes around the circle in order?
My name for it isn't very ladylike and I don't like calling it a 'jam'. It would be kind of handy to have another appropriate term to use.