What is runoff and what does it mean

Runoff is liquid, especially water or rainwater, that flows off or drains away, as in The storm sewer could not hold all the runoff from the recent rains. ... This term comes from the verb phrase run off, which can mean to drain or flow away, as in The wastewater runs off into the stream.

Explanation:

Runoff is nothing more than water "running off" the land surface.

Just as the water you wash your car with runs off down the driveway as you work, the rain that Mother Nature covers the landscape with runs off downhill, too (due to gravity). Runoff is an important component of the natural water cycle.

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