Overhang seats can arise in elections under mixed member proportional (MMP), when a party is entiteled to less seats according to party votes than it has won constituencies. These Overhang seats (for missing votes) remain with the party.
The ways to deal with overhang seats are:
Take the number of overhang seats off from the other parties' seats, E.g. Scottish Parliament
...
As of the census of 2000, there are 14,078 people, 4,578 households, and 3,731 families residing in the town. The population density is 1,322.5/km² ...