Optical scan ballots
These are paper ballots, marked by voters, either manually with (typically) pens or through the use of a ballot marking device, which can be counted by optical scanners or by hand. Voters then carry or have carried their ballots (sleeved or otherwise protected so that others cannot see their ballot selections) to a scanner. At the scanner, the ballot is unsleeved and insert it into the scanner, which detects the voters’ marks with an optical scanning element and records the votes electronically. The paper ballots are deposited into the scanner and preserved for audits and recounts. They are sometimes called “mark-sense” ballots, these are used widely for absentee voting and vote-by-mail, and also for emergency and provisional voting.
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