I’m a bit late in recognizing the new abbreviation of the Court of Justice of the European Union, CJEU, rather than the earlier ECJ.

There’s a useful document in the House of Commons Library – Standard Note SN/IA/3689: The European Union: a guide to terminology, procedures and sources, last updated 16 March 2011.

Here’s the page where you can download it.

EC or EU law? Treaty of Rome or Treaty of Lisbon? First, Second or Third Pillar? Acquis Communautaire? Court of Justice or Court of Human Rights?
This Note aims to clarify some of the terminology used to describe the institutions, laws and procedures of the European Union. It also provides links to useful sources of information on the EU.

It’s 14 pages in length. It contains links for further research and reading.

9 European Courts
There are two main European Courts. Media reports sometimes confuse the two, alleging that the EC/EU has ruled on something when it is in fact the Court of Human Rights that has ruled, and vice versa.
• The Court of Justice of the European Union (CJEU) is the EU court which rules on alleged breaches of EC law and the Treaties. CJEU judgments (by convention not spelt with an ‘e’ as in ‘judgements’) can be found on the CURIA website..
•
The European Court of Human Rights is the Council of Europe court which rules on alleged breaches of the European Convention on Human Rights. ECHR judgments can be found on the HUDOC website.

Another point this document mentions is that since the Treaty of Lisbon, all EU legislation can be called EU law. This has been a point of contention in some sections of the ITI, because apparently at a talk they were advised not to use the term ‘EU law’ (although there are books on the subject).

4 EC law or EU law?
Former Article 281 of the Treaty of Rome as amended (and similar articles in the ECSC and Euratom Treaties) gave the EEC ‘legal personality’. That is to say, only the then EEC and its successor, the EC, had rights and obligations under international law allowing it to adopt laws and treaties. Former Article 282 of the EC Treaty conferred upon the EC “the most extensive legal capacity accorded to legal persons” under the national laws of the Member States. The EU did not have this status, and so strictly speaking we should have referred to ‘EC law’ and not to ‘EU law’ in most instances until December 2009.
Until November 1993, when the TEU came into force, the EU’s Official Journal (OJ) references were to ‘EEC’ law. After 1993 the OJ used ‘EC’. The OJ distinguished between EC laws and CFSP or Police/Judicial Cooperation Decisions, which were Second and Third Pillar (EU) instruments. For example, a Council Regulation was written as ‘Council Regulation (EC) 850/2005’ in the Official Journal; a Commission Directive was written as ‘Commission Directive 2005/37/EC’.
All these instruments are now EU instruments. Since the granting of “legal personality” to the EU under the Treaty of Lisbon, it is now technically and legally correct to refer to EU law and EU Treaties.

We still write those Directives and Regulations with ‘(EC)’ etc., but it seems that retrospectively they are all EU documents.

Via Jaanike Erne ideas on europe and Grahnlaw

LATER NOTE (June 2012) – perhaps this is clearer, from the UK parliament site:

9. The CJEU is the collective term for the European Union’s judicial arm,[8] but the single institution consists of three separate courts, each enjoying its own specific jurisdiction. Generally speaking the three courts’ jurisdictions are defined by the types of cases they hear or by the status of the litigant bringing the action and whilst the CJEU does not operate on a formally hierarchical framework like, for example, the UK court structure, it is nevertheless split into three tiers. Forming the upper tier is the Court of Justice (CJ) which was formerly known as the European Court of Justice (ECJ); beneath the CJ is the General Court (GC) which was formerly known as the Court of First Instance (CFI); and the third tier consists of the Civil Service Tribunal (CST), which in the words of the Treaty constitutes the EU’s single “specialised court”.[9] Francis Jacobs, former Advocate General at the Court of Justice and presently Professor of Law at King’s College London, considered this structure a good one.[10]

The term for the court as a whole is CJEU – the term ECJ used to be used both in this collective sense and to refer to the Court of Justice. Now, the collective abbreviation is CJEU and the Court of Justice abbreviation is CJ (sometimes ECJ, I imagine).