A flown flag is a flag that has historic meaning, sentimental value, or has been flown for a special occasion. Flown flags have traditionally been handed out by dignitaries during special occasions and events.
Since 1937 the United States Capitol Flag Program has been taking requests for flags to be flown over the US Capitol Building at the request of the United States Congress and United States House of Representatives as a service.
References
Flown flag Wikipedia(Text) CC BY-SA