There is a difference from someone that is a "jogger" VS a "runner". A jogger is doing it to get in shape or lose weight. A runner has the underlying question "How fast and how far can I go?"
There is a "feeling" a runner is striving to achieve, and once you do, it's like a drug, something you want again and again. The "feeling" occurs when you can easly run your normal training run and the whole time you feel like are floating, moving effortlessly over the ground. You're relaxed, at ease with your body. Afterward you know you could have run futher and you want to run futher to hold onto that feeling longer. That is the moment you have moved from jogger to RUNNER.
It is a great feeling and I can still remember when I hit that point, when I became a runner. I was in high school, running on the bypass road in Williston. The hot blacktop road shimmered with heat as my teamates and I ran a steady pace, mile after mile, our legs in perfect cadence, floating over the pavement, the only sound was our breathing and feet hitting the pavement. It was so relaxing and felt like I could keep that pace up forever. I KNEW that I was experiencing something that many people would never feel and I wanted to feel it again as soon as it was done. That "feeling" is why I run, you don't get that feeling on every run, some days are struggles, but it only takes a one great run to erase several bad runs. That is why I run.