LONDON/BRUSSELS (Reuters) - Nearly five years since the Brexit crisis began, the United Kingdom and the European Union have clinched a trade deal that defines their relationship after Dec. 31. Why does it matter after all the twists and turns of Britain’s exit from the EU? 1) ATMOSPHERE - Britain formally left the EU on Jan. 31 but has been in a status quo transition period since then. The deal struck on Thursday avoids an acrimonious and economically tumultuous end to that phase on New Year’s Eve, after which the EU will deem the UK a ‘third country’. 2) TRADE - The UK will leave the EU’s single market and customs union, so the rules and regulations on trading everything from car parts to camembert cheese will change. Bilateral trade is worth around $1 trillion a year. The deal is narrow and only covers goods. Even with a deal, there will be disruption at the borders because of new customs checks and paperwork. But without one, the disruption - and anger on both sides - would have been much greater. 3) ECONOMY - After the novel coronavirus destroyed whole sectors across the Western world, neither the UK nor the EU’s 27 remaining members wanted another hit to their economies. A deal softens the blow of Brexit, though economists warn that leaving the EU’s orbit will still hurt the world’s sixth-largest economy. 4) BREXIT DIVERGENCE? - A key test for both sides of the deal will be how far it allows the UK to delink itself from the EU - the very essence of Brexit. Fundamentally, there are two rival interpretations of Brexit: for the EU’s supporters, Brexit is an act of economic lunacy that divides the West, while for Brexit supporters it is an opportunity to break free and compete. Prime Minister Boris Johnson portrays Brexit as a chance to build Britain into a fully independent economy that would be much more agile than its competitors, and so does not want to be tied into the EU’s orbit and its rules for years to come. EU powers fear that London wants the best of both worlds - preferential access to EU markets, with the advantage of setting its own rules. They say this would undermine a project that has sought to bind the nations of Europe, ruined by World War Two, into a global trading power. “Hey, is [the deal] better than where we were five years ago? Yes, it is. Is it good enough to allow us to become Singapore, the really dynamic booming economy? No,” Brexit campaigner Nigel Farage said. 5) NOT JUST TRADE - The “deal” is actually a bundle: at the centre is a trade deal but there are also accompanying deals on fishing, law enforcement, transport, legal issues and data. Law enforcement, for example, is important as the two sides share details about criminals, suspects and passports. Data is important for companies that store the data of citizens.