What are “impervious and pervious areas”?

Impervious areas are those that do not absorb rainwater.  Examples include the roof of a building, driveways, parking lots, paved playground areas, tennis courts or hard packed soil.  Pervious areas are those that absorb rainwater and primarily consist of lawns and other grassy surface areas.  While these areas do absorb rain water, pervious surface areas generate some runoff, primarily during heavy rain events.