The idea of this session is to have a physical wall at the venue to either post sticky notes or to directly write on it (e.g. whiteboard). Everybody is encouraged to ask questions or ideas that he/she wants to talk about and either propose to meet at a certain place and time to do so or post for instance a twitter account to clarify the details.
The idea is that there is a low barrier to ask questions - especially for people that are new to the conference. It can be quite intimidating to attend a conference where you know nobody but would like to talk about certain topics.
The wall itself can then be a meeting point and people can read interesting proposals and questions. If they are interested in the same thing they might join the following meeting.