It's just referred to as an 'open figure session' because there is no instructor or leader per se, rather just a group of 4-5 artists that have been attending for many years that all help run it (the group has been getting together for 25+ years!). Usually around 20 - 25 people attend each session, from college students looking for extra model time to fatten their portfolios, to retirees who's kids are all grown and they can finally take the time to make art for art's sake. Since I'm there so regularly I have become pretty friendly with most of the hosts so I help out a little and now I even bring the music every other week. It's fun! We chat, we draw, we nibble treats and sip wine - what more could you ask for? It's a great sense of camaraderie just chillin' with so many other like-minded artists up there:)
As far as the flow of the session goes, the models do about 2 1/2 hours worth of poses, including a number of two to ten minute poses and then culminating in three 20 minute poses, so all the life drawings I share are all created in 20 minutes or less. If you're curious about the goings-on or etiquette of the figure sessions, check out my slightly silly 'Figure Drawing Session Etiquette' blog/vlog.
When I first started attending last year I felt like there was no way I could get anything done in such a short time frame, but it has actually really helped me hone my skills and be more deliberate with my markings. Plus I love the naturally occurring 'unfinished' feel that is created when I literally run out of time and can't do any more.