I already explained that. To some degree.
It's when characters in a sci-fi space story have musical scores just for them. Luke's theme(when he looks at the 2 suns of Tatooine), Vader's theme, the imperial march, etc. Each piece of music is a theme for a character or group.
Wiki's : http://en.wikipedia.org/wiki/Space_Opera
Their description is ok but it describes to much Star Wars without mentionning music. This is not my opinion by the way but I read multiple times that music is an integral part of a Space Opera, specifically the themes.
However, Star Wars is the first and to my knowledge the only Space Opera so I guess Wiki's description is pretty accurate.
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You all are stil arguing about this?