Stormwater, also called storm water, rainwater, or runoff, is the water from precipitation events that is not intercepted, infiltrated, evaporated, transpired, or otherwise abstracted which is released overland or into another conveyance system.

Stormwater management, or SWM, is the application of retention, detention, infiltration or other measures to control the peak flow, runoff volume, or other aspects of stormwater. Typically, SWM is implemented to mitigate the effects of urbanization on a receiving system, by peak flow reduction, volumetric reduction, or quality control.