"Green... infrastructure is a stormwater management tool that focuses on the use of vegetation to collect and treat stormwater as opposed to using man made components such as drains, pipes and treatment plants. It essentially allows Mother Nature to do her job naturally and brings a little green benefit to the city at the same time." Arrus Farmer, for PlanPhilly.
Below: one example of "green infrastructure."
Permeable paving on an alleyway in Chicago. EPA photo.