by Adrienne Mahsa Varkiani THINK PROGRESS

CREDIT: AP Photo/Matt Dunham

Someone holds up a sign during a European Referendum “Remain” rally in London, Wednesday, June 22, 2016.

Months of furious campaigning will culminate in a significant vote on Thursday, as the United Kingdom is set to decide whether or not it will leave the European Union.

Haven’t been following the debate closely? To understand why this vote matters — and what a decision to leave the E.U. could mean — here’s a quick guide to what you should know.

What does Brexit mean?

Brexit is a combination of the words Britain and exit, referring to the U.K. leaving the E.U. Because it sounds catchy, it’s how most people are referring to the upcoming referendum on June 23, which asks voters:

“Should the United Kingdom remain a member of the European Union or leave the European Union?”

Thus, there are two sides in this referendum: Remain and Leave.

What is the European Union?

The European Union is an economic and political partnership with 28 countries in Europe that seeks to create a single market with the free movement of people, goods, and services. Currently, the E.U. has its own currency (the euro, used by 19 of those countries), its own parliament, court of justice, and a set of laws for members on issues like the environment, human rights, and consumer product safety.

The E.U. has roots in the 1952 European Coal and Steel Community, an organization that sought to avoid another world war on the continent through trade, believing that countries that do business with each other are less likely to go to war. In 1967, this turned into the European Economic Community — of which the U.K. was a member — and in 1993, the European Union.

E.U. membership is different for every country. For the U.K., that means being a member of the union while retaining its own currency (the pound) and not being a part of the Schengen Area — a group of countries that allows visitors to travel between them without passports.

What’s the Remain campaign saying?

The Remain side says that leaving the E.U. could have disastrous effects on the U.K.’s economy and security — and many experts are backing that position.

Europe is the U.K.’s most important trade partner and a significant source of foreign investment, and that’s in large part due to the union. The U.K. Treasury has warned that the country would be “permanently poorer” if it leaves the E.U.

The Bank of England has similarly warned that uncertainty about the referendum is already affecting the economy, with businesses and consumers putting off major decisions, and if the U.K. decides to leave, the value of the pound would fall drastically. The U.K. economy could also expect to lose many of the benefits it’s received from migration from the E.U. — which amounted to over £20 billion between 2001 and 2011 alone, according to one study from University College London.

In terms of national security, former MI6 Chief John Sawers has warned that leaving the E.U. would make the U.K. “less safe” because it would shut the U.K. out of “crucial” intelligence sharing with the E.U. U.K. Home Secretary Theresa May, former Chairman of the British Joint Intelligence Committee Pauline Neville-Jones, former Director General of MI5 Eliza Manningham-Buller, and Europol Chief Rob Wainwright have all said similar things.

What’s the Leave campaign saying?

The Leave campaign has urged voters to “take control” over the U.K. economy, laws, and borders. A lot of the support for leaving the E.U. comes from this idea of the U.K. currently losing control to the bureaucrats in Brussels, who are undemocratically imposing regulations on the U.K. citizen. The Leave side has continuously stressed the undemocratic nature of the E.U. and the burdensome regulations that accompany membership. Conservative MP Boris Johnson recently said that choosing to leave the E.U. could be “Britain’s Independence Day.”

Leave supporters have also made quite a big deal about the flow of immigration into the country. While the U.K. has taken in an incredibly small number of refugees compared to other countries, there are nonetheless mounting fears about the refugee crisis facing Europe — and it’s evident in the way the Leave side has campaigned.

Tell me about the crazy things that have happened during campaigning.

The craziest thing about this campaign has been the fear-mongering about immigration.

As many have noted, the rhetoric of the Leave campaign has at times been virtually indistinguishable from the rhetoric of the far-right in the U.K. The far-right British National Party has warned that remaining in the E.U. could mean that “an almost limitless number of Middle Easterners and Muslims” would pour into the E.U. through Turkey. The official Leave campaign has repeatedly made similar points about the dangers of Turkey joining the E.U.

After the shooting in Orlando on June 12, an organization campaigning on the Leave side also urged voters to act to prevent a similar attack of “Islamic extremism” in the U.K.

And in perhaps the most obvious fear-mongering, last week, the United Kingdom Independent Party (UKIP) — which is on the Leave side of this campaign — released a new poster that many said was eerily similar to Nazi propaganda in the 1930s. The word “Breaking Point” in all red was set over a 2015 photo by Getty Images photographer Jeff Mitchell of thousands of refugees near the Slovenia-Croatia border, and thus part of the Schengen Area.

Nigel Farage, the leader of UKIP, has not apologized for the poster — claiming he “can’t apologize for the truth” — but he has apologized for the timing.

The same day, Labour MP Jo Cox was shot and killed while she was meeting with constituents. Cox, who was an outspoken advocate of the benefits of immigration and diversity and favored remaining in the E.U., was killed by a man linked to white supremacist movements who gave his name in court as “Death to traitors, freedom for Britain.” Asked to confirm his name, the suspected murderer again said, “My name is death to traitors, freedom for Britain.”

Unsurprisingly, many are pointing to the rhetoric of hate and fear among the Leave campaign as contributing factors in Cox’s murder. German Chancellor Angela Merkel urged politicians to moderate the language they use during the rest of their E.U. referendum campaigns.

“The exaggerations and radicalisation of part of the language do not help to foster an atmosphere of respect,” she said shortly after Cox’s murder. “That’s why we all value democratic game rules. And we know how important it is to draw limits, be it in the choice of speech, in the choice of the argument, but also in the choice of partly disparaging argument.”

Austrian Chancellor Christian Kern also told the Guardian the killing was “only further proof of how quickly violent words can turn into violent deeds.”

Who’s going to win?

Honestly, no one’s really sure. Recent polls reveal that it could be either side.

I scrolled all the way down and don’t want to read this piece. Show me a funny video breaking this down instead.

Fair enough. John Oliver explains the whole thing pretty well in the video below, and even includes a sing-along song for you to enjoy.