What does "regime" mean?

Regime: (Hydraul.) The condition of a river with respect to the rate of its flow, as measured by the volume of water passing different cross sections in a given time, uniform régime being the condition when the flow is equal and uniform at all the cross sections. The ancient régime, or Ancien régime Etym: [F.], the former political and social system, as distinguished from the modern; especially, the political and social system existing in France before the Revolution of 1789.