1. A ballot that has been issued to a voter but will not be cast, usually because it has been incorrectly marked or impaired in some way.
Source: Election Terminology Glossary - Draft, National Institute of Standards and Technology (NIST), https://pages.nist.gov/ElectionGlossary/
2. Ballot that has been voted but will not be cast.
Source: Glossary of terms database, U.S. Election Assistance Commission, https://www.eac.gov/glossary/; ELECTIONS: The Nation’s Evolving Election System as Reflected in the November 2004 General Election, U.S. Government Accountability Office, https://www.gao.gov/assets/160/157713.pdf; ELECTIONS: The Nation’s Evolving Election System as Reflected in the November 2004 General Election, U.S. Government Accountability Office, https://www.gao.gov/assets/160/157713.pdf
3. A spoiled ballot will not count in an election. It is a ballot (optical scan, absentee, emergency or provisional) that a voter returns to election officials to cancel after he or she has made an error. The concepts of “cancellation” and “spoiled ballot” are often linked, in that statutory limits on the number of ballots a voter may spoil are sometimes interpreted as applying to the number of cancellations a voter can make on a DRE (Direct Recording Electronic voting machine), and especially, a DRE equipped with a VVPAT (Voter-Verified Paper Audit Trail).
Source: COUNTING VOTES 2012: A State by State Look at Voting Technology Preparedness, Verified Voting Foundation, Rutgers School of Law - Newark Constitutional Litigation Clinic & Common Cause Education Fund, https://countingvotes.org/sites/default/files/CountingVotes2012_Final_August2012.pdf