The Olympic flag reference article from the English Wikipedia on 24-Apr-2004
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Olympic flag

The Olympic flag is raised during the opening ceremonies of each Olympic Games, and lower during the closing ceremonies. The flag uses the ancient symbol of the Olympic Games (five interlocking rings); blue, yellow, black, green, and red respectively on a white field uncovered by Baron Pierre de Coubertin in 1892. The flag was first raised during the VIIth Olympiad in Antwerp, Belgium in 1920. It is fabled that every nation that has an Olympic team has at least one of their national colours in the Olympic flag.

The rings are said, thematically, to represent the habitable continents: Europe, Africa, Asia, Oceania, and the Americas.