Since you mail in an absentee ballot, it seems like mail-in ballot is just a convenient alternative for people who always forget the word absentee. And though the terms are often used interchangeably, there is technically a difference.

Up until the Civil War, American voters were generally required to vote at their local polling stations in person. But when states realized this would prevent hundreds of thousands of soldiers from voting in the 1864 presidential election, they started passing laws to let them send in their ballots instead. As The Washington Post explains, state legislatures have since broadened these laws to include other citizens who can’t make it to the polls on Election Day: people who are traveling, people who have disabilities, people attending college away from home, etc. Because these voters are all physically absent from the polls for one reason or another, their ballots are known as absentee ballots.

Some states require you to meet certain criteria in order to qualify for an absentee ballot, while others don’t ask you to give a reason at all (which is known as “no-excuse absentee voting”). Since this year’s general election is happening during a pandemic, many states have temporarily adopted a no-excuse policy to encourage everyone to vote from home. But even if you don’t need to provide an excuse, you do usually need to request an absentee ballot.

According to Dictionary.com, mail-in ballot is a more general term that can refer to any ballot you send in. It’s often used when talking about all-mail voting, when states send a ballot to every registered voter—no request necessary. Oregon and a few other states actually conduct all elections like this, and several other states have decided to do it for the upcoming presidential election. But even though you don’t have to send in an application requesting a mail-in ballot in these situations, you do still have to be registered to vote.

Because voting processes are mostly left up to the states, there’s quite a bit of variation when it comes to what officials call ballots that you don’t cast in person. You could see the term mail-in ballot—or vote-by-mail ballot, or advanced ballot, or something similar—on an application for an absentee ballot, and you could hear absentee ballot used in a conversation about all-mail voting.

No matter what you call it, you should definitely mail one in for this election—here’s how to do that in your state.