Preliminary statement: The evolution of what is today the European Union (EU) from a regional economic agreement among six neighboring states in 1951 to today's hybrid intergovernmental and supranational organization of 28 countries across the European continent stands as an unprecedented phenomenon in the annals of history. Dynastic unions for territorial consolidation were long the norm in Europe; on a few occasions even country-level unions were arranged - the Polish-Lithuanian Commonwealth and the Austro-Hungarian Empire were examples. But for such a large number of nation-states to cede some of their sovereignty to an overarching entity is unique.
Although the EU is not a federation in the strict sense, it is far more than a free-trade association such as ASEAN, NAFTA, or Mercosur, and it has certain attributes associated with independent nations: its own flag, currency (for some members), and law-making abilities, as well as diplomatic representation and a common foreign and security policy in its dealings with external partners.
Thus, inclusion of basic intelligence on the EU has been deemed appropriate as a separate entity in The World Factbook. However, because of the EU's special status, this description is placed after the regular country entries.
Source: CIA World Factbook - This page was last updated on January 20, 2018