Specifically it refers to the University Of Chicago and several economists who taught there like Milton Friedman and George Stigler. More generally it refers to the economic "school of thought" generated by those economists and their colleagues which promotes deregulation and allowing market forces to shape the economy rather than governmental meddling.
Ironic that the same city should produce both his time's principal advocate of free markets in Friedman, and also the current principal advocate of turning America into the Federal Union of Socialist Workers and Peasants Democratic Collectives in Obama, is it not?
Two Nobel laureates, I leave it as an exercise in the obvious to identify which one of the two won his Nobel prize for Economics.