According to this science, flag is an emblem. It can be a national one or of any other allegiance. But it's only one side of the meaning. Flags can be used for signalling at a distance. I would be prepared to lay money that you don't know what vexillology is. It is a form of communication that was widely spread in Rome. It's also used as a semaphore symbol code in the Navy. One more interesting fact about flags is their designing.