Short answers, pulled from the story.
A country is a distinct area of land with a government that functions as a sovereign state, an unrecognized state, a constituent country, or a dependent territory. There is no universal agreement on the number of countries in the world, and The Economist wrote in 2010 that any attempt to find a clear definition runs into a thicket of exceptions and anomalies.
There is no universal agreement on the number of countries, partly because several states have disputed sovereignty and some non-sovereign entities are commonly called countries. The ISO 3166 standard currently comprises 249 countries, 193 of which are sovereign states that are members of the United Nations.
The declarative theory, outlined in the 1933 Montevideo Convention, holds that a sovereign state can exist even if no other country recognizes it, provided it has a permanent population, a defined territory, a government, and the ability to enter into relations with other states. The constitutive theory holds that a state becomes a legal entity of international law only if it is recognized as sovereign by at least one other country.
A constituent country is a separate polity within a sovereign state that may also be considered a country in its own right. Examples include England, Scotland, Wales, and Northern Ireland within the United Kingdom, and Denmark proper, the Faroe Islands, and Greenland within the Danish Realm.
A country's name can hold cultural and diplomatic significance, so changes often reflect shifts in government or the end of colonial rule. Upper Volta changed its name to Burkina Faso to reflect the end of French colonization, while North Macedonia's name was disputed for years due to a conflict with the Macedonia region in Greece.
The World Bank uses the Atlas method to classify countries by gross national income per capita into low-income, lower-middle-income, upper-middle-income, and high-income economies. For the 2020 fiscal year, low-income economies had a GNI per capita of $1,025 or less in 2018, while high-income economies had $12,376 or more.