Citizen journalism is news distributed, not by the pros, but by any (usually) unaffiliated citizen with a mobile phone and/or internet connection.1 In addition to this definition, citizen journalism is many things: a way to bypass censorship, a way to publicize the views and opinions of people who may not otherwise have a say, a way for the public to participate in the distribution of the news they and their fellow citizens will consume, etc.
On December 30, 2006 Saddam Hussein was executed, hanged by the Iraqi Special Tribunal for his crimes against humanity. The Iraqi government actually released an official video of the execution, respectfully excluding the exact moment of death from their version of the event.
However, shortly after the execution, another video surfaced and this one (supposedly taken and distributed by one of the guards with a mobile phone) showed everything, including the moment of death. (This is a link to the full unofficial video. VIEWER DISCRETION IS ADVISED). This is a particularly graphic example of citizen journalism.
(Image from hellasashell.wordpress.com)
1. Ralph E. Hanson, Mass Communication: Living in a Media World, 3e (Washington, DC: CQ PRess, 2011), 365.