suc·cess səkˈses/ noun the accomplishment of an aim or purpose. "the president had some success in restoring confidence"
Success to me is a personal feeling of accomplishment. It's feeling okay with where you are and what you've done.
My definition: doing something you wanted to do. Binary test: Did you do a thing? Did you want to do that thing? If you answered yes to both questions, you are a success at that thing. Did you want to read that book, and so you read it? You're a success at reading that book! Did you want to pass that class with a C- or better, and you got a C-? You're a success at passing that class with a C-! Separately, being "a success" means doing something someone else wanted you to do. It doesn't matter if you read all those books and passed all those classes: if nobody wanted you to do those, nobody's going to label you a success. You had success, but you are not one. Similarly, if you live up to everyone else's expectations but not your own, you can be "a success" who has not had your own success.