What is Brexit?
Brexit refers to Britain's exit from the European Union.
It's not the only portmanteau of this kind, with Grexit having preceded it. Last week there was talk of a possible Frexit if Marine le Pen's National Front were to rise to power, and there's even been murmurs of a "Gerexit".
In fact, if your country hasn't had "xit" spliced with its name, it's probably missing out.
Why is everyone talking about it now?
Things suddenly ramped up this weekend, after David Cameron revealed the date of the referendum, and which way the cabinet will be voting.
Some of his most senior ministers, including justice secretary Michael Gove, leader of the Commons Chris Grayling, work and pensions secretary Iain Duncan Smith and culture minister John Whittingdale immediately held a press conference to say they were backing Brexit.
This was then followed over the weekend by more "rebel" behaviour from the likes of Conservative mayoral candidate Zac Goldsmith and - crucially - charismatic outgoing mayor Boris Johnson.
When is the EU referendum?
The main reason it's suddenly become a hot topic is that we now know when the UK will be going to the polls to decide the country's fate: the date of the EU referendum is 23 June.
What are the key issues?
Cameron has spent the last few months in Europe trying to secure a reform package that will encourage Brits to remain in the UK. There are four main areas of focus:
1) Reducing benefits for migrants to discourage them from coming to the UK
2) Cutting red tape on business - and gaining assurances that UK firms would have to relocate into Europe
3) Exempting Britain from "ever closer union" with the EU
4) Protection for countries such as the UK that do not have the euro
He revealed what he had secured at the weekend, but for many there was just not enough meat on the bone to convince - particularly those who were already sceptical.
Those who are pro-Brexit argue that the UK is being weighed down by European red tape and has lost its sovereign ability to decide its own laws; they claim that migration is far higher than it would be if we came out, particularly from parts of Eastern Europe and that the UK's membership costs around £24m a day - effectively that we are subsidising poorer or worse-off parts of Europe.
They also argue that plenty of other smaller countries such as Switzerland and Norway trade effectively with Europe and the rest of the world without being part of the bloc.
Those who are pro-Remain (or "Bremain" if you can stomach it) warn that the UK's economy would suffer as both trade with Europe and the rest of the world would suffer; that prices of food would rise, as well as the cost of travelling to Europe; that our standing in the international community would decline and we would lose important bargaining power in trade deals, political brokering and other global issues.
They also note that as the UK has never been part of the Schengen Agreement - which allows free movement through members' borders - coming out of the EU would not affect immigration to the degree that Brexiteers suggest. But it would make it more difficult to hire throughout the EU, which would hurt business.
It could also have the unintended consequence of triggering another Scottish independence referendum, which the government narrowly won in 2014.
Who is backing in/remain?
David Cameron, of course, is backing the remain camp, as is chancellor George Osborne, home secretary Theresa May, foreign secretary Philip Hammond and business secretary Sajid Javid. In fact, most of the cabinet has rallied behind Cameron, although there are a number of defectors as noted above.
Labour is very firmly in the "in" camp - in fact, 214 out of 231 MPs have said they will be voting to remain in the EU. If you're not sure which way your MP is leaning, you can find out here.
The Lib Dems are in - in fact Lib Dem leader Tim Farron made a little aside swipe at Boris Johnson for his current position.
.@timfarron: "Boris has had more positions on Europe than the Karma Sutra."— Lauren Fedor (@LaurenFedor) February 21, 2016
Outside of politics, there is also plenty of support, not least from big business, with many chief executives from FTSE 100 companies having put their name to a letter of public support for Cameron. Banks including Standard Life have warned it could damage the UK economy while fund managers have warned it will cause "carnage".
Who is backing out/Brexit?
Ukip has been banging the drum on this issue for years, so it's no surprise that leader Nigel Farage and the party's one MP Douglas Carswell are pro-Brexit.
But no longer is Ukip is a lone voice: Conservative front benchers have joined the likes of influential backbencher Jacob Rees-Mogg in backing the Leave campaign.
One of the main problems plaguing the Out campaign has been its divisiveness until now: there's been plenty of in-fighting which has stopped there being a coherent message.
What about the people who matter?
Polls are notoriously untrustworthy (let's face it, they confidently predicted we'd be getting Ed Miliband for PM last year) but for what it's worth, the numbers of real-life people (aka voters) in favour of leaving the EU have been ticking up over recent months.
The latest poll, published on Friday ahead of the reforms being agreed, put Leave in the lead.
Can we trust what we're being told by either camp?
As this article explores, the numbers are being heavily twisted. In short, data being used by both sides should be taken with a pinch of salt. Legendary fund manager Neil Woodford certainly seems to agree.
Is it going to get ugly?
You could say that. Already people who have come out on one side or the other have been told their careers are effectively over.
Mud is being slung in all directions with supporters of both sides being variously described as "parochial", "little Englanders" and "protectionist".
Why does it matter?
This is being touted as a once-in-a-lifetime decision. And, unlike the Scottish independence referendum, this one really will stick. They say.