This equation represents the measurement of an instantaneous rate of change as h approaches zero. In many ways, it is the original definition of the mathematical derivative and represents  one of the biggest steps of Newton and Leibniz in their (independent) developments of modern day calculus.

Citation and Reference

“This is a pedagogical review of recent results on the interactions of central massive black holes with stars very near them, focused on the black hole in the center of the Milky Way.”
\cite{Alexander}