1. the act of classifying.
  2. the result of classifying or being classified.
  3. one of the groups or classes into which things may be or have been classified.
  4. Biology. the assignment of organisms to groups within a system of categories distinguished by structure, origin, etc. The usual series of categories is phylum (or, especially in botany, division), class, order, family, genus, species, and variety.
  5. the category, as restricted, confidential, secret, or top secret, to which information, a document, etc., is assigned, as by a government or military agency, based on the degree of protection considered necessary to safeguard it from unauthorized use.
  6. Library Science. any of various systems for arranging books and other materials, especially according to subject or format.


  1. systematic placement in categories
  2. one of the divisions in a system of classifying
  3. biology
    1. the placing of animals and plants in a series of increasingly specialized groups because of similarities in structure, origin, molecular composition, etc, that indicate a common relationship. The major groups are domain or superkingdom, kingdom, phylum (in animals) or division (in plants), class, order, family, genus, and species
    2. the study of the principles and practice of this process; taxonomy
  4. government the designation of an item of information as being secret and not available to people outside a restricted group

1772, “action of classifying,” noun of action from Latin stem of classify, or from French classification. Meaning “result of classifying” is from 1789.


  1. A systematic arrangement into classes or groups.
  2. The systematic grouping of organisms into categories on the basis of evolutionary or structural relationships between them; taxonomy.

  1. The systematic grouping of organisms according to the structural or evolutionary relationships among them. Organisms are normally classified by observed similarities in their body and cell structure or by evolutionary relationships based on the analysis of sequences of their DNA. See more at cladistics Linnean. See Table at taxonomy.

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