Longman Dictionary of Contemporary English
Wiktionary
n. (context US English) A vote made remotely, especially a postal ballot, cast by a voter unable to be present in person.
WordNet
n. (election) a ballot that is cast in absentia (usually mailed in prior to election day)
Wikipedia
An absentee ballot is a vote cast by someone who is unable or unwilling to attend the official polling station or to which the voter is normally allocated. Numerous methods have been devised to facilitate this. Increasing the ease of access to absentee ballots is seen by many as one way to improve voter turnout, though some countries require that a valid reason, such as infirmity or travel, be given before a voter can participate in an absentee ballot.
Usage examples of "absentee ballot".
Hosea Blackford said when Flora came back to their apartment after voting: he was still registered in Dakota, and had cast an absentee ballot.
Florida style, meant that the rules governing acceptance or denial of your absentee ballot depended on what county you were from.
But Al Gore lost the election, lost the recount, lost the absentee ballot returns, and lost all the manual recounts that could be completed within seven days.
For example, George Bush had talked to the governors of various states about their absentee ballot numbers, and Jeb Bush could tell Ellis how outstanding precincts had voted in his elections.
He admitted that he had lived in Tulsa for more than ten years but still voted by absentee ballot in Madison County in every election, though he was no longer a legal resident there.
Anyhow, she'll be home for Election Day, and Barry'll vote by absentee ballot.
Kirk might even send in his landowner's absentee ballot, for once.
Anyhow, shell be home for Election Day, and Barryll vote by absentee ballot.