What is the difference between a ‘country’ and a ‘regional patent office’ in the context of foreign priority claims?

In the context of foreign priority claims, there’s an important distinction between a ‘country’ and a ‘regional patent office’:

• Country: A sovereign nation that has its own patent system and can issue patents directly.
• Regional Patent Office: An intergovernmental organization that processes patent applications on behalf of multiple member countries.

The MPEP states: The right of priority may be based upon an application filed in a foreign country or in a regional patent office. (MPEP 213)

Regional patent offices, such as the European Patent Office (EPO) or the African Regional Intellectual Property Organization (ARIPO), allow applicants to file a single application that can potentially lead to patent protection in multiple member countries.