It's just running.  Like with anything; it can mean different things to different people.

Agreed.  It can also mean different things to the same person.  If I want to zone out, I can throw on the iPod and hit the pavement.  If I want to multi-task I can hop on the TM and catch the news or a ballgame.   If I want to "be in the moment"  I can bust out a fast-paced trail run where a momentary loss of focus can lead to big trouble.

We're seen as odd by non-runners, but I'm surprised more people don't run.  We were not born to fly, and although some of us are quite at home in the water we were not born to swim, despite the 39-week aquatic head-start.  The human musculoskeletal system is built for running.  

The glutes, quads and hamstrings are some of the largest muscles in the body; our limbs swing rhythmically to help us maintain balance; our knees, ankles and elbows bend in just the right direction.  

Running stimulates the pleasure centers of the brain; it awakens the appetite; it helps put us to sleep.  

Running requires no special tools or equipment.  It is a primal function that gave us an evolutionary edge.  And as many of you have stated, it's good medicine ... for whatever ails us.