[workingandtired]

From the wikipedia page for nation [http://en.wikipedia.org/wiki/Nation]:

The word "nation" is sometimes used as synonym for:

State (polity) or sovereign state: a government which controls a specific territory, which may or may not be associated with any particular ethnic group

Country: a geographic territory, which may or may not have an affiliation with a government or ethnic group

Thus the phrase "nations of the world" could be referring to the top-level governments (as in the name for the United Nations), various large geographical territories, or various large ethnic groups of the planet.

In general, whenever I come across the word "nation" I assume it's being used colloquially to refer to "nation-state", unless the context is specifically related to ethnic nationalistic identities.