Democratic deficit This is a term used to describe what some people say is a gap between the powers of the EU and the power of its citizens to influence EU decision-making.
Critics of the EU argue that its institutions lack transparency and that its elected officials, the MEPs, have much less influence than the unelected EU commissioners.
DG This stands for Directorate-General. There are 27 DGs in the EU, covering different policy areas, ranging from transport to external relations. There are, in addition, departments dealing with services such as translation, personnel and the fight against fraud.
Each DG is headed by a commissioner, who is assisted by the director-general (also referred to as a DG) and a group of civil servants.
The DG's civil servants draft proposals for new EU laws, which are then presented by the relevant commissioner in a weekly meeting attended by all commissioners, called the "college".
The college of commissioners takes a collective decision on whether to take the proposal forward.
ECB The European Central Bank based in Frankfurt is responsible for implementing European monetary policy.
It works together with the national central banks of the EU states forming the European System of Central Banks.
Its goal, as defined by the Maastricht Treaty, is to maintain price stability in the eurozone countries.
EFTA This stands for European Free Trade Association, which promotes free trade and economic integration between Iceland, Liechtenstein, Norway and Switzerland.
EFTA was set up in 1960 as an alternative group for those countries which were not, or did not want to be, part of what was then the European Economic Community.
Originally there were seven EFTA countries: Austria, Denmark, Norway, Portugal, Sweden, Switzerland and the UK.
Austria, Denmark, Portugal, Sweden and the UK went on to join the EU.
Economic and Monetary Union (EMU) is the official name of the monetary union that has resulted in the single currency, the euro.
It was formed in three stages.
In the first stage, EU member states agreed to the free movement of capital and closer co-operation between their central banks.
During the second stage, the European Central Bank and the European Monetary Institute were established. EU members also had to sign up to the convergence of their economic and monetary policies.
In the third and final stage, exchange rates were fixed and the single currency was introduced, first on the foreign exchange markets and later in the form of euro notes and coins.
Sixteen EU member states have reached the final stage and are currently using the euro. Denmark and the UK opted out of the third stage.
Sweden rejected adoption of the euro in a referendum and is not working towards reaching the third stage.
Bulgaria, the Czech Republic, Estonia, Hungary, Latvia, Lithuania, Poland and Romania have not yet reached stage three.
Enlargement The EU has gone through six expansions since it came into being in the 1950s, the sixth taking place in 2007 when Romania and Bulgaria joined.
Before they can become members, candidates must fulfil conditions known as the Copenhagen criteria.
Croatia, Macedonia and Turkey are officially recognised as candidates.
ESDP The European Security and Defence Policy is the area of EU policy covering military co-operation between member states.
ETS The EU's Emissions Trading Scheme (ETS) was launched in 2005. Its purpose is to reduce industrial emissions of the greenhouse gas carbon dioxide (CO2). Permits for emitting CO2 are distributed under a system of national allocations. The permits are traded - so big polluters can buy extra ones from greener enterprises.
Eulex This is the European Union Rule of Law Mission in Kosovo, a civilian mission set up to strengthen the rule of law in the Balkan territory, which broke away from Serbia.
Eulex staff oversee the police, courts and customs service, ensuring that they are free from political interference and comply with international standards. About 1,400 Eulex police officers are deployed in Kosovo.
Eurojust Eurojust was created in 2002 to improve the investigation and prosecution of cross-border and organised crime.
Based in The Hague, it is composed of 27 National Members, one from each EU Member State. Members are prosecutors, judges, or senior police officers.
European Commission The European Commission is more than simply the EU's civil service. It is the only body that can propose legislation.
It is sometimes seen as the driving force behind European integration, but is ultimately under the control of the member states.
The commission is made up of 27 commissioners, each with responsibility for a policy area, such as agriculture or enlargement.
Commissioners are appointed by the member states, and are usually senior politicians. However, their job is to act in the general European interest, not to advance the interests of their own country.
European Council This is the name given to the regular meetings - sometimes called summits - which bring together the EU countries' heads of state or government and their foreign ministers. The president of the European Commission also attends.
The decisions taken at the European Council meetings have a major impetus in defining the EU's general political guidelines.
Each meeting is usually preceded by an exchange of views with the president of the European Parliament. The European Council is convened at least four times a year, with all meetings held in Brussels.
European Court of Auditors This is the body that keeps track of EU money so that citizens know where their money goes. Its aim is to improve the efficiency of EU financial management.
The court audits the EU accounts and the implementation of the budget, providing the European Parliament and the Council of Ministers with a statement on the accounts' reliability.
European Court of Human Rights The Court of Human Rights, based in Strasbourg, is the court of the Council of Europe.
It oversees the European Convention on Human Rights established in 1950. This protects the fundamental rights of people living in Council of Europe member states.
The court is not an EU institution and has no powers of enforcement.
The convention is also separate from EU law, though it serves as a basis for it and provides precedents which are often followed.
European Court of Justice The Court of Justice rules on disputes over EU treaties and other EU legislation. Its decisions are binding on EU institutions and member states.
A member state may be taken to court for failing to meet its obligations under EU law; big fines can be imposed for non-compliance with the court's rulings.
It is made up of senior judges from each member state, who hold office for a renewable term of six years. The court also hears actions brought by individuals seeking damages from European institutions, or the annulment of EU legislation which directly concerns them.
European Parliament The parliament is the only directly elected body in the European Union.
It holds regular plenary sessions in Strasbourg, and has a secretariat in Luxembourg, but members of the parliament do most of their work in Brussels. This is where they examine draft legislation in committees and consult with the Commission and Council of Ministers.
The parliament has the power to sack the Commission, it holds hearings on new commissioners, and has the last word on about half the spending in the EU annual budget.
Its powers have been steadily increasing. Most EU legislation now needs the approval of both parliament and the Council of Ministers before it becomes law.
Europol This is the European Law Enforcement Organisation. Based in The Hague, it tries to improve co-ordination between police forces across the EU to target international organised crime.
It combats drug trafficking, illegal immigration and people trafficking, counterfeit operations, smuggling of stolen vehicles and money laundering. Increasingly, it also deals with financial crime and cybercrime in cases involving two or more EU member states.
Federalism A system of government where several states pool sovereignty in some areas but keep their independence.
A federation has a central government, in addition to the governments that head its constituent states.
Arguments about EU integration often focus on the extent to which member states should transfer sovereignty to supranational bodies.
Frontex Frontex is the EU agency tasked with ensuring border security. Based in Warsaw, its full title is the European Agency for the Management of Operational Co-operation at the External Borders.
Frontex also helps member states train border guards and gives technical and operational help to secure the EU's external borders.
GAERC This stands for the General Affairs and External Relations Council - the monthly meeting of EU foreign ministers. They deal with important foreign policy issues and help set the agenda of European Council meetings.
Harmonisation This is a core principle of the EU. It means bringing national laws into line with one another, to prevent discrimination and ensure a level playing field. Mostly it takes the form of directives, which establish minimum obligations while allowing states some leeway. EU regulations - less common - are binding laws which must be uniform throughout the EU.
High Representative The High Representative for the Common Foreign and Security Policy was introduced as part of the Amsterdam Treaty. It said the High Representative would assist the Council in foreign policy formulation and implementation, and - when requested by the Council presidency - by "conducting political dialogue with third countries".
The Lisbon Treaty has beefed up the role, by merging it with that of the EU external affairs commissioner. The new post has the title "High Representative for Foreign Affairs and Security Policy". Baroness Catherine Ashton from the UK is the new High Representative, with a five-year term. She will have a say over the EU's foreign aid budget and will head a new 5,000-strong EU diplomatic corps.
IGC An Intergovernmental Conference or IGC is a long-running conference between the governments of EU member states.
The aim of the IGC is to produce a treaty - for example the Maastricht Treaty. These are in fact not new pieces of legislation but amendments to the Treaty - the founding Treaty of Rome, signed in 1957.
Ioannina compromise This clause was added to the rules for qualified majority voting (QMV) to make it impossible for a very small number of the EU's most populous states to prevent a decision from being adopted. The new voting system will only apply from 2014 - a result of Polish pressure.
Under the clause - amended during the Lisbon Treaty negotiations - a blocking minority must comprise at least four member states. If that does not happen, QMV will be deemed to have worked even if the population criterion is not met. Under Lisbon, a Council of Ministers decision requires a "double majority" - ie, the support of 55% of member states representing at least 65% of the EU's population.