Elemental Celerity is Shantotto's Glint learned from Terra's Staff (XI). It costs one Soul Break bar per use but can only be used three times per battle, grants a 20% boost to the user's lightning attacks and triples their casting speed for two turns.
Classical elements typically refer to ancient concepts similar to the modern states of matter: earth (solid), water (liquid), air (gas) and fire (plasma). Classical elements are the simplest form of existence, of everything in existence. Many philosophies and worldviews believe in classical elements.
Celerity is an archaic noun that means "swiftness" or "speed".