Dewey decimal classification

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A system used in libraries for organizing nonfiction publications into subject categories corresponding to three-digit numerals, with further specification expressed by numerals following a decimal point.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun 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