What is "Oberwolfach style"? I've read the following in a description of a workshop:


  We have about 15 participants and seek an “Oberwolfach style” with a relatively low density of talks.


I couldn't find anything about this style in Internet. But I found out that there is The Mathematical Research Institute of Oberwolfach, and according to Wikipedia


  It organizes weekly workshops on diverse topics where mathematicians and scientists from all over the world come to do collaborative research.


But the sense of this “Oberwolfach style” is still vague to me.
This is indeed a reference to the Mathematisches Forschungsinstitut Oberwolfach (Oberwolfach Mathematics Research Institute), a conference center in the small German town of Oberwolfach.

The Institute has developed a rather idiosyncratic style of meetings.  The most common events are weeklong workshops on specific topics, whose participants are invited by the organizers.  Speakers are chosen from among the participants on just one or two days' notice.  The talks are indeed relatively "low density", perhaps 4 or 5 x 45-minute talks per day, so not all participants will give talks.  Long periods are left unscheduled to encourage informal discussion and collaboration.  

The conference center is isolated and so most people don't leave the campus during the week.  Participants are housed and fed onsite and meals are communal.  As Aru says, there are also measures to "encourage" a more social atmosphere: seating is assigned and changes from meal to meal, and Internet access is not available in the guest rooms until 10pm or so (edit: Najib Idrissi's comment below suggests that this policy has changed).