A life with your family by your side, earning your livelihood without much of problems, spending time with people who need help from you and also giving back to the society with whatever little you can do is being successful. A life without any debt from anyone or any institution is also a main thing here. This would be my real definition of success. Like somebody rightfully said, " Success is measured by others and satisfaction is measured by yourself". So try and lead a satisfactory life which itself will be a successful one.
This is getting into a lot of areas that tend to be philosophical. You can say you are a success if you "make a lot of money", "have a high ranking job", "hold a lot of patents", or some other metric. I myself have two standards I like: One very practical, and one very theoretical.
On the practical side, I earn a living for myself and my family. I have had enough to buy a house, cars, and provide a college education from my three kids. Is it mansion? No. Are the cars all Rolls Royce? Not close. Was it Harvard or MIT my kids went to? No (at least, not so far!) ;) But we have always had medical care, food, and enough. This is so much more that so many in the world have that I would be foolish to ignore this "success".
On the theoretical side, I look back to my college days and a English professor teaching a honor's English course. He looked at the talent in that room, and challenged us to "give back". "Noblesse oblige" (Noble Obligation) is the idea that if you have a skill that can benefit others, they you have an obligation to USE that skill to other's benefit. I have done that where I can, and would like to think that my work not only has let me make a living, but has benefited others. I sometimes have "put in extra work" and "made sure it will work for those I don't see"... but that is both the duty and satisfaction of "Noblesse oblige".
These are not the only measures that people use (to be sure). But doing what you can for yourself and others has not been a bad measure for me. Hopefully you use these, or find ones for yourself. :) Best of luck, and enjoy the search!