10/20s are a little hard to "grok" when reading about them, but they are awesome ways of kicking off conversations.
The 10/20 format was made popular by Grok Conference in South Carolina. Of all of the meetup attendees, someone can ask for either 10 or 20 minutes for a design topic discussion. We'll start the last one just after 8 and then switch out to our normal chatting.
The person chosen can use the time in multiple ways: talk the whole time, talk for part of the time and open to feedback, open up a question to the group for discussion, etc.