The way I define fulfillment is the feeling you get when you do something for someone without expecting anything in return, this is call service. We came to the world to serve others, to give. That is the only way to get fulfillment. You can be filthy rich, extremely handsome, undeniable smart, super healthy and still be miserable inside if you are not serving others.
The way I define purpose is how you serve; it is putting all your human being resources to the purpose of serving. It is using your values, belief, intelligence, motivators and unique talent to create ways to serve.