Final answer:
The term 'peripheral countries' in relation to Greece, Ireland, Portugal, and Spain refers to their geographical position in Europe and their less industrialized economies which rely more on agriculture and raw materials. They suffer from brain drain and have historically lower GDP per capita than central European nations.
Step-by-step explanation:
The reason why Greece, Ireland, Portugal, and Spain are sometimes referred to as the eurozone's "peripheral countries" is that they are situated in the peripheral parts of Europe and have economies that are less industrialized compared to their central European counterparts. These countries, including the agrarian regions of southern Italy, have been facing economic struggles, especially since the global recession that began in 2007. They are characterized by a lower gross domestic product (GDP) per capita, reliance on agriculture and the provision of raw materials, and a higher propensity for the emigration of skilled individuals, known as brain drain.
Geographic isolation has also played a role; for instance, the Iberian Peninsula, consisting of Spain and Portugal, is separated from the rest of Europe by the Pyrenees mountains. This has historically limited the flow of ideas and contributed to different economic and social development. In contrast, regions such as northern Italy are more industrialized and urbanized than their southern counterparts, which are more rural with fewer industries. The eurozone's core countries, by comparison, tend to have advanced industrial bases, higher incomes, and are heavily involved in economic globalization.