a final election to resolve an earlier election that did not produce a winner
"The governorship will go to the voters again in November because no candidate received a majority of votes in the primary runoff."
That portion of precipitation or irrigation on an area which does not infiltrate or evaporate, but instead is discharged from the area.
"Heavy rains caused significant runoff to flow over the dry fields and into the nearby creek without soaking into the soil."
In plain English: Runoff is water that flows over land instead of soaking into the ground after it rains too hard.
"The heavy rain caused dirty water to flow over the street and into the storm drain."
Usage: Runoff refers specifically to water that flows over land surfaces rather than soaking into the ground or evaporating. It commonly describes stormwater drainage issues in urban areas or agricultural nutrient loss caused by excess irrigation discharge.
Runoff comes directly from combining the verb run with the word off. It originally referred to water flowing away after rain or snowmelt before evolving into its modern political meaning for votes cast in a second election.