Customs Union, Single Market, Withdrawal Agreement... we've been bombarded with complex terminology by politicians for months. But what does it all mean? And why does it matter?
Let's break it down.
This is the agreement between Theresa May and the other 27 EU countries, which deals with the terms of the UK's exit.
It was supposed to be the starting point for the next round of discussions — the future relationship between post-Brexit Britain and the EU. The UK parliament has, however, failed to agree to its terms, and now, Theresa May plans to return to Brussels to ask for changes.
Perhaps the most contentious part of the Withdrawal Agreement is the Backstop.
Central to the peace process on the island of Ireland was the commitment that no hard border would exist between the Republic of Ireland and Northern Ireland.
Until now, both countries have been EU member states, but after Brexit, a land border would appear between the Republic (EU) and Northern Ireland (UK).
The Backstop was designed as an insurance policy to prevent this becoming a hard border if the EU and UK could not agree on the terms of a new relationship.
In other words, it aims to prevent border checks, fences and other infrastructure formally dividing the two countries.
In effect, it would achieve this by keeping the UK in the EU Custom's Union, with Northern Ireland following some of the rules of the Single Market. More on those two below.
Critically, the UK could not choose to leave the Backstop on its own, as the EU would also have to agree. Critics say this could trap the UK indefinitely, but the EU argues it is central to protecting the peace process on the island of Ireland.
The EU is both a Customs Union and a Single Market.
So, let's break down the differences:
The Customs Union scraps taxes (tariffs) on goods moving between countries.
It also means that member states put the same tariffs on goods entering the union from external countries.
Being part of the Customs Union means countries cannot negotiate their own trade deals.
Remaining part of the Customs Union is controversial for some Brexit supporters, as they argue it would undermine the UK's ability to negotiate new trade deals.
The Single Market goes much further than the Customs Union.
It allows for the free movement of not just goods, but people, wealth (capital) and services as well.
It also imposes common rules so that consumers in different EU countries have the same rights and companies can operate under the same conditions.
Particularly contentious in the Brexit debate was the free movement of people — Prime Minister Theresa May said ending it was one of her "red lines".