In English, World is rooted in a compound of the obsolete words were, man, and eld, age; thus, its oldest meaning is "Age of Man." World can refer to the domain of discourse, but it can also mean many other things:

Physical locations

World dymaxion map

World is often synonymous with the planet Earth (especially when capitalized: the World). World map is a map of the surface of the Earth.

The word "world" is sometimes used as a synonym for planet; for example, Mars and Jupiter are two worlds within the solar system.

It is sometimes used to refer to the entire Universe. This is less common now that knowledge of space is more commonplace; however, it is still used vaguely in this sense (as in "the whole wide world").

Other senses

World can be used in less literal terms; for example, when describing two people with very little in common, one can describe them as "living in two different worlds." When a person refers to the "end of the world," that person usually means "the end of everything I am familiar with."

In another religious sense, in Christianity the world refers to the fallen and corrupt world order of human society outside the community of believers. The world is frequently cited alongside the flesh and the Devil as a source of temptation that Christians should flee.

World can also refer to a fictional setting, for example the world of Star Trek or the world of The Lord of the Rings. See fictional realm.

In knowledge engineering and knowledge level modeling, the term world refers to a consistent state of beliefs. A system's world is the knowledge that system has about its environment.

In Native American mythology, the Fifth World is the coming world that will exist after the current world.

First World, Second World, Third World

Mercator map (Large 2 MB).

The terms First World, Second World, and Third World were used to divide the nations of Earth into three broad categories. Originally, First World referred to capitalist societies, Second World to centrally planned Communist ones, and Third World for the non-aligned countries. The latter were mostly developing countries, many of these are located in Africa, Latin America, and Asia. They are often nations that were colonized by another nation in the past.

In the context of the Cold War:

First World refers to nations that were within the United States' sphere of influence - e.g., the NATO countries of North America and Western Europe, Japan, and some of the former British colonies such as Australia, New Zealand, and South Africa.

Second World refers to nations within the Soviet Union's sphere of influence, e.g. Warsaw Pact countries. Besides the Soviet Union proper, most of Eastern Europe was run by satellite governments working closely with Moscow. This term may or may not also refer to Communist countries whose leadership were at odds with Moscow, e.g. China and Yugoslavia.

Third World refers to nations within neither sphere of influence and were often members of the Non-Aligned Movement. After World War II, the First and Second Worlds struggled to expand their respective spheres of influence to the Third World. The militaries and intelligence services of the United States and the Soviet Union worked both secretly and overtly to influence Third World governments, with mixed success.

There were a number of countries which did not fit comfortably into this neat definition of partition, including Switzerland, Sweden, and the Republic of Ireland, which chose to be neutral. Finland was under the Soviet Union's sphere of influence but was not communist, nor was it a member of the Warsaw Pact. Austria was under the United States' sphere of influence, but in 1955, when the country again became a fully independent republic, it did so under the condition that it remained neutral.

With the 1991 collapse of the Soviet Union and the fall of Leninist Communism, the term Second World largely fell out of use — though Third World remains popular. The remaining Communist countries either became more isolated from the world economy, as in North Korea and Cuba, or began integrating capitalist concepts such as private enterprise into their societies and forging new trading ties with external capitalist economies, as in Vietnam and China.

In more recent use, the term First World refers to developed nations, while Third World, in contrast, refers to developing/undeveloped nations.

There is also the less commonly used term Fourth World, often used to refer to nations that lack any national representation at the UN, but that may enjoy representation at UNPO — indigenous peoples living within or across state boundaries.