It's called intenional election fraud. Theft by the dead.

Group claims thousands of 'voters' are deceased
Group sues over voter registration records
Members of a conservative advocacy group claim they’ve uncovered thousands of votes that were registered in deceased people’s names and say the Secretary of State left them on the voting rolls.
5 EYEWITNESS NEWS took the names of a handful of dead voters and tried to find out why they're listed by the state as having voted and found tired election workers, long hours, and confusing rules may be more to blame than outright fraud.
Julie Webster died in August 2006, but she voted two years later on Nov. 4, 2008. Her widow Henry Webster did not know until 5 EYEWITNESS NEWS told him that Secretary of State Mark Ritchie lists his wife as having voted last fall.
"I’m here to tell you, there's no malice on my end," he said. "[Election officials and I] had a two-way conversation that my wife had died and that she won't be coming in. So I wrote deceased."
But an election worker mistakenly counted that as a voter who showed up to cast a ballot.
Dan McGrath with the group Minnesota Majority is critical of the Secretary of State's office for not removing dead voters from the rolls.
"They can't possibly know what happened in this election," he said. "There is a systemic problem that is making it impossible to determine whether there's fraud."
Deputy Secretary of State Jim Gelbmann was shown five dead voters found by Minnesota Majority. The five voters Minnesota Majority provided to us died during the tenure of both a DFL and Republican Secretary of State.
In each case, Gelbmann produced documentation that he says shows mistakes, not fraud, were at fault.
"I would venture—put my reputation on—the fact that there are very few, if any, people impersonating dead people," he said. "You’re going to have human error. We're doing our best to correct that human error."
The group plans to announce Wednesday that 2,812 dead people may be listed as having voted—either by error or fraud.