"The word "deliberation" means to consider an issue carefully, usually to make a decision or statement about it. At its best, "deliberation" means that a full range of relevant facts, factors, perspectives, options and consequences are being considered in a way that generates new understandings and possibilities.
Deliberation assumes a certain quality of conversation that supports people learning or reasonably shifting their perspectives as they proceed. Public deliberation implies, in addition, a certain amount of shared concern for the common good and usually a growing appreciation for the complexity of the situation, as people learn more about it and take more into account.
"Citizen deliberation," as the phrase is used in this site, means that people holding diverse perspectives are talking together respectfully about public concerns. All the participants' views are being heard in ways that add up to greater understanding than any of them had when they began the conversation. Usually there's a significant amount of face-to-face dialogue, although it is sometimes electronically augmented in some way. The term citizen deliberation suggests that the citizens involved will generate a statement or decision or activity that will benefit the larger community in some way." (http://www.co-intelligence.org/deliberation.html)
1. Tom Atlee, on The Varieties of Citizen Deliberation:
"Many forms of citizen deliberation are in use today. For example,
- Citizen deliberative councils convene temporary groups of usually 10-50 randomly selected ordinary citizens to consider public concerns and report back to the community (or country) and/or to public officials.
- Study circles bring together small groups of people to discuss briefing materials -- often used throughout a community to deal with a community issue, and then participants are convened at the end to form action groups
- National Issues Forum organizes topical deliberative conversations through civic organizations around the U.S. and then shares the results with public officials.
- America Speaks convenes hundreds or thousands of people using high-tech connections to integrate and prioritize their diverse perspectives.
- Environmental roundtables bring together diverse stakeholders to creatively address controversial land use and other issues.
- In deliberative polling, citizens are surveyed before and after they deliberate, to see how the deliberations have changed their opinions.
- Future search conferences convene representative stakeholders from all parts of a community to look at their shared history, the forces currently shaping their shared lives, and visions they can all agree on and work towards.
- Holistic Management weaves all the important people and resources relating to an issue together into the pursuit of a shared goal which covers all the relevant dimensions of the issue.
- Our Media Voice Citizen Feedback Forums bring citizens together in live broadcasts to discuss how broadcast media serve their community."
2. According to Bernard Guibert:
According to Yves Syntomer, it also has four characteristics (or rather, four models inspired by different values):
- 1) the scientific argumentation (the brahmin model)
- 2) negotiation (a merchant model)
- 3) polemics (a warrior model)
- 4) sophistics (a manipulative, rhetorical model)
Modes 1 and 3 are based on a general interest and lead to higher synthesis. Modes 2 and 4 are based on the differential interests of the parties.
The first model combines rational debate in search of truth and a selective elitist principle: it is the liberal ideal of representative democracy.
Deliberative democracies requires that any citizen speaks for himself, in dialogue with others. This dialogue has to be organized according to certain procedures.
In the interplay between egalitarian and elitist principles, with the latter dominating in representation, what has to happen is a reversal.
Bibliography, recommended by Tiago Peixoto:
"David Lazer is the co-author of two of these papers. If you don’t know it already, Stuart Shulman’s work is definitely worth checking out. Thamy Pogrebinschi is probably one of the people to look out for in the coming years in the field of Participatory Democracy." 
Lazer, David, Sokhey, Anand E., Neblo, Michael A. and Esterling, Kevin M., Deliberative Ripples: The Network Effects of Political Events (August 10, 2010). 
Neblo, Michael A., Esterling, Kevin M., Kennedy, Ryan, Lazer, David and Sokhey, Anand E., Who Wants to Deliberate – and Why? (September 15, 2009). HKS Working Paper No. RWP09-027. 
Stuart W. Shulman, 2009. “The case against mass e–mails: Perverse incentives and low quality public participation in U.S. federal rulemaking,” Policy & Internet, volume 1, number 1, article 2. 
Pogrebinschi, Thamy, The Squared Circle of Participatory Democracy: Scaling-up Deliberation to the National Level (2012). APSA 2012 Annual Meeting Paper.