The countries of the EMU. That is, the group of European countries, members of the EU, that adopted the common currency, the euro. See baffling pigs.
The 12 countries of Europe that have combined their currencies into a single currency, the Euro. They have separate sovereignties but a combined central bank, the ECB.
The group of twelve countries that have combined their currencies into a single currency (Euro). They still have separate sovereignties, but also have a combined central bank (ECB) which handles economic policy issues for them as one group.