What Does the "O" in Big-O Notation Stand For

What does the "O" in big-O notation stand for?

A) The "O" stands for "on the order of," which is a reference to the order of complexity of the work of the algorithm.
B) The "O" stands for "Organization of," which is a reference to the organization of complex functions at work in the algorithm.
C) The "O" stands for "on the ontology of," which is a reference to the structure of the algorithm itself.
D) The "O" stands for "on the openness of," which is a reference to the ability to discern from code how the algorithm functions.