What was the Swine Flu outbreak of 2009?

In the spring of 2009 a new virus that causes a new influenza illness -- A-H1N1/09 (swine flu) -- was discovered in Mexico. It started as a local outbreak and quickly spread into an epidemic throughout Mexico, then the US and eventually all of North America. By the time of the fall 2009-2010 flu season, it had spread far and wide around the world and qualified as a true pandemic affecting people in every country of the world. We are currently (2011) in the post pandemic phase with fewer and fewer isolated outbreaks. See the questions below for more information.