Can someone articulately explain what Swine flu is?

I'm not worried about it. The cases in the U.S. have been mild, so I think the ones that died in Mexico must have had other health problems. I think the media is covering it a lot because this strain of Flu is very different than what we've known before 1. it's ping from person to person instead of pig to person and 2. it's effecting adults instead of the very young and very old. This could be important in future strains of Flu.