A configuration of the European Union in which some of the countries integrate more fully than others. The adoption of the euro by only some of the countries that were then in the EU was the major exa [..]

This refers to the theoretical possibility that, in future, a particular “core” group of EU Member States may decide to move faster than others along the road of European integration . It is already possible for a group of EU countries to work together more closely than others under an arrangement known as “enhanced co-operation” .