What does "International Government Organization (IGO)" mean?

An IGO (sometimes called an "Intergovernmental
Organization") is an organization that is created by states (instead of by private
individuals like an NGO is) for a specific reason.  IGOs tend to be made to combat
problems that are important to the states that create
them.

One major IGO is the North Atlantic Treaty
Organization (NATO).  NATO was created by the US and by countries of Western Europe
during the Cold War.  It was an IGO because it was created by these states but was not
part of the government of any one of them -- it was its own, relatively independent
organization.  NATO's purpose was to deter the Soviet Union and to otherwise increase
the security of Western Europe and the US.

The World Trade
Organization (WTO) is another important IGO.  It was set up by various states to
regulate trade among them.  It is meant to reduce the likelihood of trade disputes and
to, thereby, increase world prosperity.

IGOs are important
to IR theorists because they increase the amount of contact between countries and (to
liberals) decrease the likelihood of conflict between countries.