What is the third world?

This was to be the month that leaders of the third world were to meet in Baghdad, Iraq.

The trouble is that Iraq and its neighbor, Iran, are at war with each other and the Iranians threatened they would sabotage the conference if it were held in Iraq. As a result the Iraqis decided it would be wiser if the third world heads of states met in India instead.

''Third world'' is the term used to describe nations that are mostly in the poor, developing countries of Africa, Latin America, and Asia. But the third world also includes some rich oil nations in the Middle East. This is a useful reminder not to think of all third world nations as poor.

The third world got started back in the 1950s when five prominent statesmen decided that the nations of the world should not be pulled between two political camps. These two camps were the East and the West. In a sense, East and West make up two different worlds even though they are never called ''first world'' or ''second world.''

By West we mean countries like the United States, Canada, and all the nations of Western Europe, as well as Australia and New Zealand. And Japan, even though it is geographically in the East, is called part of the West. This is because its government and the way it runs its industries and trade follow the model of the West. The West sometimes is also known as the free world or the democratic world.

By contrast, the East refers to the communist systems of the world. That includes the Soviet Union, China, Eastern Europe, and even Cuba although geographically Cuba is in the West.

In 1974 Deng Xiaoping defined the Chinese belief that the socialist camp no longer existed -- that the ''first world'' was that of the two superpowers, the ''second world'' was that of the developed nations, and the third world was that of the developing nations.

The founders of the third world, a world separate from the East and the West, were Prime Minister Jawaharlal Nehru of India, President Sukarno of Indonesia, President Gamal Abdel Nasser of Egypt, Marshal Tito of Yugoslavia, and Prime Minister U Nu of Burma.

Their idea was that there should be a separate bloc of nations that would be independent of either East or West. Because they wanted to be separate, or independent, they also came to be called nonaligned countries. That means they were not aligned, or linked, or attached to either the East or West. Sometimes they are viewed as the world's neutral countries.

The difficulty is that there are countries that belong to the third world that do not consider themselves nonaligned. And there are nonaligned countries that don't see themselves as part of the third world. There is lots of overlapping between the two, and in many people's minds they represent the same thing.

By using the term third world it is easy to think of the world's having three overall political systems. That is democracy (countries of the West), communism (countries of the East), and third world, or neutral and non-aligned. Unfortunately it's not quite as easy as that. Some so-called third world or nonaligned countries are closer to the East; some to the West. There's a big difference, for instance, in the nonaligned or third-world camp between Singapore (pro-West) and Cuba (pro-East).

These days we are hearing less about East and West and third world and more about North and South. North stands for rich countries. They can be East or West. Both the United States and the Soviet Union, though they have very different societies and governments, are on the North side. That is because North stands for the wealthier and more powerful countries north of the equator. In other words, the Northern Hemisphere.

South stands for south of the equator or the Southern Hemisphere. It includes mostly poor countries in tropical and subtropical climates. Here again the definition is somewhat loose. Australia and South Africa are very much in the Southern Hemisphere. But their wealth means they are classed with the North.

Because there is such a great gulf between the rich and the poor nations, there are experts who feel the big problems in the future will have to do more with the issues that separate the so-called North and South than with the issues that now divide East and West.