What is the meaning of Constituent_country?

Any country that is a subdivision of a larger sovereign state.

An administrative division of the United Kingdom: one of England, Scotland, Wales and Northern Ireland.

A land of the Kingdom of the Netherlands, of which there are four: the Netherlands proper (comprising its twelve European provinces and the three BES Islands of the Caribbean Netherlands: Bonaire, Sint Eustatius, and Saba) and the three Caribbean island countries of Aruba, Curaçao, and Sint Maarten.

A sovereign country as a member of a larger organization.

Source: wiktionary.org