Purpose can be defined from an individual, or from a collective but the common definition is that Purpose is the meaning of one's life. Since our lives consist of
complicated social heirarchies, intertwined with communal and individual primal needs a simple driving Purpose is often times beyond the grasp of our conscious minds. Those among us whom have found a harmony
between their life's work and passions appear genuinely content, and often times have reserves of energy that inspires those near them.
Agent Smith, a fictional character from "The Matrix" has some comments on Purpose.
From The Matrix Reloaded, Neo meets the new Agent Smith