I can still remember my grade 6 music teacher explaining to the class that "All music is sound, but not all sound is music" (Something my teenage daughter still doesn't understand - but that's another subject)
I hate to have to break this to you boys - "All kilts are skirts, but not all skirts are kilts.
Having said that, I cling ardently to the the fact that "IT'S A KILT" I wouldn't be caught dead in a skirt!