Spoiled ballot

A spoiled ballot or spoilt vote is a ballot which suggests that the voter did not followed the provided instructions. A ballot is often considered "spoilt", "spoiled"," void", "null", "informal", "invalid" or "stray" if a law declares or an election authority determines that it is invalid and thus not included in the vote count. This may occur accidentally or deliberately. The total number of spoiled ballots in a United States election has been called the "residual vote". In Australia, such votes are generally referred to as "informal votes", and in Canada they are referred to as "rejected votes".

In some jurisdictions, the number of spoiled ballots are counted and reported.

Instant-runoff voing

In ranked-choice/instant-runoff voting (IRV), the concept of "spoiled ballot" gets a bit complicated:

Overvote

The above is an example of an "overvote" in a ranked-choice/instant-runoff voting election

An overvote in an IRV election occurs when a voter marks two candidates in a single column/rank. For example, if a voter marked both Janie Smith and Aaron Jones as his first choice, his ballot would not count in the election. Likewise, if a voter correctly ranked his first choice but marked two candidates in the following column, only the first choice would be tabulated.

Undervote

The above is an example of an "undervote" in a ranked-choice/instant-runoff voting election

An undervote in an IRV election occurs occurs when a voter skips two or more columns or rankings. For example, if a voter picked Janie Smith as his first choice, skipped his second and third choice and selected another candidate as his fourth choice, his ballot would not count in the election after the first round.