folklore - the unwritten literature (stories and proverbs and riddles and songs) of a culture

faerie, faery, fairy, sprite - small, human in form, playful, having magical powers

leprechaun - a mischievous elf in Irish folklore

sandman - an elf in fairy stories who sprinkles sand in children's eyes to make them sleepy

radio frequency - an electromagnetic wave frequency between audio and infrared

electromagnetic spectrum - the entire frequency range of electromagnetic waves