An unconference is an open space conference. Essentially, it is a realisation that everyone in the room has something to contribute, and so presents a format whereby the knowledge in the room can be gathered, rather than having one person talking while the rest sit in the audience on social media.
It came about as a reflection that most of the value of a traditional conference happens in the breaks over coffee, and informal networking and meeting. No one talking at you, but rather with you.
This could be "How can open data solve the water crisis", which was the topic of the unconference held with the Department of Water and Sanitation in Johannesburg in 2016.
Experts from the citizenry, government, civil society, academia, the media and business are invited to participate.
Every participant is introduced to the theme and the structure of the day (it helps to have a great facilitator that is used to running this sort of gathering). They are then asked to each write down two key topics that they would like to speak about each on an A4 page, and stick these on the wall (you need a wall). If there are 80 participants, it means that once this is done you have 160 discussion topics on the wall.
All participants are then invited to form the agenda by uniting similar topics and forming more robust discussion sessions in the process. If you have an all day unconference, there is typically space for around 48 one hour discussion sessions (six 1-hour sessions in 8 areas), so 160 topics has to become 48 sessions.
The discussion sessions begin. They happen in a circle of chairs in the room, where the person responsible for the central topic acts as a moderator and introduces the topic, and facilitates discussion. A note taker is appointed to record the discussion.
The final step is having enough note capturers to capture the notes in full after each round of sessions, which means that by the end of the day these can all be printed out and put up on the wall. This should mean that, in our example, 48 key topics concerning the central theme are there for everyone to engage with. This should also provide a great resource to be taken forward in the design of your open data project.