Here's what it means to me from a creative artist's point of view.
I don't think success exists in the finishing-post type sense. Instead I see little stepping stones on a journey of discovery. A stepping stone is reached each time something (anything) which educates, entertains, causes new thoughts and imaginations, is brought from the realm of ideas and placed in front of others.
Finishing a work is a success. Presenting that work is a success. Disseminating the work is a success. Everything learned and put into practise on how to refine and hone each stage is a success. Most of all keeping the joy alive is the greatest success.
Of course financial reward is desirable for me and I would count that as a success if I ever manage to get that to a liveable level. Each time somebody buys my work I get a little leap of happiness and I count that as a success too.
I expect that as people get success in one form they look towards the next level a bit like a platform computer game like Super Mario. Anyone who ever finished a game like that will know the horrible anti-climax and how it isn't half as much fun as the getting there.
I think the trick is to keep enjoying the little victories and always have something to aim for, which is what is so lovely about creative work because as long as the main attraction is the work then the possibilities are endless.
The problem is when people can't enjoy their achievements by always valuing the next stepping stone more than the last and then they get frustrated and dissatisfied. Or they get worried they can't replicate the previous 'success' and get stymied.
This blog post was inspired by reading Linda Gillard's blog post here - Indie Authors, How Do You Define Self-Publishing Success?