The GUAM is a regional organization of four post-soviet countries. Full name of the organization is The GUAM Organization for Democracy and Economic Development. Letter "G" stands for Georgia, "U" for Ukraine, "A" for Azerbaijan and "M" for Moldova. From 1999 to 2005 the organization was called GUUAM. The second "U" was for Uzbekistan. Other organizations of post-soviet countries: CIS, Baltic Assembly and etc. Improving transport, trade and economics between this countries are main goals of the organization. Also, the GUAM cooperates on "international and regional security" and maintains a joint peacekeeping force.
Source: Wikipedia