To me, being successful means...
Living a fulfilled, balanced life where I make a difference.

My definition of success has changed over time. 
When I was in high school, I thought I had to do what was expected, in the right order, and on schedule to be successful. Now, thirty-ish years later, I know that the fact that I took a different path (put myself through college, graduated in my early thirties) means that I have a true understanding of what's important. I value that journey.