pilot whale: small dark-colored whale of the Atlantic coast of the United States; the largest male acts as pilot or leader for the school
dolphin: any of various small toothed whales with a beaklike snout; larger than porpoises
dewey decimal classification: a system used by libraries to classify nonfictional publications into subject categories; the subject is indicated by a three-digit numeral and further specification is given by numerals following a decimal point; publications are shelved by number