There was a Louisville, KY songwriter's group that held regular guitar pulls. I believe it meant that song circle had one guitar passed around and everyone played one of their songs when it was their turn. Sort of a one instrument song circle. Makes sense from a perspective of wanting people to listen to a new song. Not as much sense if you want to have people play along with your songs. I find the term itself interesting. If you can imagine one person finishing up their song and the next person getting the guitar to play his, before the last notes had faded from the last song. I should mention, I never went to one, so I could be wrong.