Meaning

1. That portion of precipitation or irrigation on an area which does not infiltrate or evaporate, but instead is discharged from the area.
2. Dissolved chemicals, etc, included in such water.
3. A second or further round of a competition, after other competitors (often all but the last two) have been eliminated.
4. A second or further round of an indecisive election, after other candidates (often all but the last two) have been eliminated.