When something goes from one place to another by accident, especially when it's something bad.
Spillover can make people think of problems or things they don't want.
Examples:
The spillover from the sink made a big mess on the floor.
The spillover from the factory polluted the river.
We don't want any spillover from the bad stuff.
The spillover from the party went into the street!
The spillover from the volcano reached the next town.
The spillover from the bad place made the good place bad too.