Haven’t a clue about Brexit? Here’s our guide to the key words

Acquis communautaire

Aka community acquis. The entire body of European laws: all the treaties, regulations and directives passed by the institutions of the European Union, plus all the rulings of the European Court of Justice (see below). Every member state has incorporated the acquis into its legal system.

Article 50

The formal mechanism for exiting the EU: the clause in the 2007 Lisbon treaty that allows any member state “to withdraw from the union in accordance with its own constitutional requirements”. The two-year article-50 talks, which among other things must settle citizens’ rights, the question of the Irish Border and the UK’s exit bill, are in effect the divorce talks.

Citizens’ rights

The rights and protections offered to all EU citizens under EU law, including free movement and residence, equal treatment and a wide range of other rights related to work, education, social security and health.

Cliff edge

The consequence of leaving the EU, its single market and customs union without a future trade deal lined up. This could mean big tariffs on some UK exports, British goods no longer accredited for sale on the continent, planes grounded, lengthy customs checks at ports, and administrative and legal chaos.

Customs union

EU members (plus Turkey, Andorra, Monaco and San Marino) trade without customs duties, taxes or tariffs between themselves, and charge the same tariffs on imports from outside the EU. Customs-union members cannot negotiate their own trade deals outside the EU, which is why leaving it – while with luck negotiating a bespoke arrangement – has been one of the UK government's Brexit goals.

European Council/European Commission

The European Council, headed by Donald Tusk, is the gathering of heads of state or government that sets the bloc's priorities and strategic goals. The commission, headed by Jean-Claude Juncker, is often called the EU's civil service but is more than that: its 28 member-appointed commissioners formally initiate EU legislation.

European Court of Justice

The Luxembourg-based ECJ rules on disputes over EU treaties and legislation; cases can be brought by governments, EU institutions, companies or citizens. Leaving the court’s jurisdiction has been one of the UK government’s requirements for Brexit.

EEA/Efta

The European Economic Area is made up of the EU's single market plus three European Free Trade Association members – Iceland, Liechtenstein and Norway – which trade freely with the single market in exchange for accepting its rules. Switzerland is in Efta but not in the EEA; bilateral accords give it special access to the single market. The four Efta countries are not in the customs union; they can negotiate trade deals with third countries, such as China.

Four freedoms

The fundamental pillars of the EU’s single market: free movement of goods, capital, services and people.

Free trade agreement

Typically long and complex to negotiate, an FTA is an agreement between at least two countries to co-operate on reducing trade barriers, such as import quotas and tariffs, so as to increase the trade of goods and sometimes services between them. An FTA between the UK and the EU will define the two parties’ future relationship after the divorce under article 50.

Great Repeal Bill

A piece of legislation that will transpose, at a stroke, all existing EU legislation affecting the UK into its domestic law to avoid a legal black hole and prevent disruption the day after the UK leaves. The Westminster parliament is then meant to “amend, repeal and improve” each law as necessary – a gargantuan task.

Hard Brexit

A hard Brexit would take the UK out of the EU’s single market and customs union and end its obligations to respect the four freedoms, make big EU budget payments and accept the jurisdiction of the European Court of Justice: what Brexiteers mean by “taking back control” of UK borders, laws and money. It would mean a return of trade tariffs, depending on what (if any) FTA were agreed.

No deal

Like “cliff edge”, except worse. No deal implies slamming the door on the article-50 divorce talks, which would make the prospect of a future FTA extremely remote. The chaos that would ensue is difficult to exaggerate.

Reste à liquider

This is the the sum of the UK’s outstanding financial commitments – commitments that have been agreed to in past EU budget negotiations but have not yet translated into payments. Defining this amount – the UK’s exit bill or divorce settlement – could be a major issue in the article 50 talks. The phrase translates from French as “remains to be settled”.

Single market

The EU’s single market is more than a free-trade area. It aims to remove not just the fiscal barriers to trade (tariffs) but also the physical and technical barriers (borders and divergent product standards), by allowing as free movement as possible of goods, capital, services and people. In essence it is about treating the EU as a single trading territory.

Soft Brexit

A soft Brexit, which not officially defined, would keep the UK in the single market, the customs union or both. It could be achieved along the lines of the Norway model (see EEA/Efta) or via a free trade agreement but would require concessions on free movement, European Court of Justice jurisdiction and budget payments. Brexiteers do not consider a soft Brexit as really leaving the EU.

Transitional deal

An agreement designed to bridge the potentially lengthy gap between the end of article 50 talks, when the UK leaves the EU, and the start of a future free-trade agreement. Both sides recognise such a deal may be necessary (the UK calls it an “implementation phase”) to avoid the cliff edge outlined above, but agreeing terms could be difficult: the EU wants it to be as short and sharp as possible.

World Trade Organisation headquarters, in Switzerland

WTO terms

Without a free-trade agreement, trade between the UK and the EU would happen under the rules of the 164-member World Trade Organisation. This could be expensive (for example, the WTO tariff on cars would be 9.8 per cent, and on lamb 40 per cent) and might raise major practical and logistical problems around things such as product approval and customs checks.

– (Guardian News and Media)