cathode-ray tube: a vacuum tube in which a hot cathode emits a beam of electrons that pass through a high voltage anode and are focused or deflected before hitting a phosphorescent screen
gas-discharge tube: a tube in which an electric discharge takes place through a gas
apple of discord: (classical mythology) a golden apple thrown into a banquet of the gods by Eris (goddess of discord--who had not been invited); the apple had `for the fairest' written on it and Hera and Athena and Aphrodite all claimed it; when Paris (prince of Troy) awarded it to Aphrodite it began a chain of events that led to the Trojan War