In the context of The Great Simplification, human labor can be thought of as the spiritual and physical exercise of will, for the purposes of either creating something tangible or achieving some kind of goal. It is the intelligence of humans and the motivation of individuals to work together in order to reliably and efficiently obtain the desired result. It is an ongoing process of iteration and experimentation, continuously pushing the boundaries of capability while expanding the scope of understanding. Human labor can truly be said to be the primary determinant of our collective progress.
See also: renewable energy, economic growth, population growth, economic system, education system