Absentee voting is the act at which a person accomplish is citizen obligation of voting but by means different of attending the official polling station, either because the person is unwilling or unable to attend it. Voting using a ballot obtained from an officer in person or by mail is to vote without attending the official polling station, therefore, this is an example of absentee voting. Military and oversea voters are examples of people that could vote using absentee voting means.
Is that the professor's reason for not discussing Jefferson...he owned slaves? I assumed you asked the professor? I can see no reason why Jefferson shouldn't be discussed. If any other person is discussed during that time frame, well, sorry...they all owned slaves and that is an invalid excuse imo.