Classification in its simplest terms, means putting together things or ideas that are alike, and keeping separate those that are different.
p. 1; Partly cited in Jens-Erik Mai (2010) Classification in a social world: bias and trust Journal of Documentation Vol. 66 No. 5, 2010. p. 640; Also cited in (Bawden, 1991). - Classification and indexing in science (1958) - Chapter 1: The need for classification