Dublin Core Elements

Title | Creator | Date | Subject | Publisher
Type | Description | Contributor | Format | Source
Rights | Identifier | Language | Relation | Coverage

4.3. Subject and Keywords

Label: Subject
Element Description: The topic of the resource. Typically, subject will be expressed as keywords or phrases that describe the subject or content of the resource. The use of controlled vocabularies and formal classification schemes is encouraged.
Guidelines for creation of content:
Select subject keywords from either the Title or Description information. If the subject of the item is a person or an organization, use the same form of the name as you would if the person or organization were a Creator, but do not repeat the name in the Creator element.

In general, choose the most significant and unique words for keywords, avoiding those too general to describe a particular item.
This element might well include classification data (for example, Library of Congress Classification Numbers or Dewey Decimal numbers) or controlled vocabularies (such as Medical Subject Headings or Art and Architecture Thesaurus descriptors) as well.

Examples
<META NAME="DC.Subject" CONTENT="Aircraft leasing and renting">
Subject="Dogs"
Subject="Olympic skiing"
Subject="Street, Picabo"

Qualifiers for DC.Subject

    From LC
      Scheme:
        (Unqualified: Keyword is default)
        LCSH (Library of Congress Subject Headings)
        MeSH (Medical Subject Headings
        AAT (Art and Architechture Thesaurus)
        LCNAF (Library of Congress Name Authority File): for names used as subjects
        DDC (Dewey Decimal Classification)
        LCC (Library of Congress Classification)
        NLM (National Library of Medicine Classification)
        UDC (Universal Decimal Classification
      Type: Not necessary

    From UK

      Scheme:
        Internal
          The information provided is not part of an external coding system and the coding should be qualified by an accompanying TYPE from the list below. This is the default scheme value if the scheme is not explicitly stated.
        LCSH
          Library of Congress Subject Heading.
        UDC
          Universal Decimal Classification.
        DDC
          Dewey Decimal Classification.
        NLM
          National Library of Medicine.
        MeSH
          Medical Subject Headings.
        Colon
          Colon Classification.
        JEL
          Journal of Economic Literature Classification
        RCHME
          RCHME/English Heritage Thesaurus (ISBN 1-873592-20-5)
        AAT
          Art & Architecture Thesaurus
        ULAN
          Union List of Artist's Names
        TGN
          Thesaurus of Geographic Names
        ICONCLASS
          ICONCLASS
        SHIC2
          Social History & Industrial Classification
        TGM1
          LC Thesaurus for Graphic Materials I: Subject Terms
        MSC
          Mathematical Science Classification
        YKL
          Finnish Public Library Classification
        SAB
          Swedish Library Classification
      Type
        Keyword
          A simple, unconstrained list of comma separated keywords and/or keyphrases. This is the default type value if the type is not explicitly stated.
        Notes
          Miscellaneous notes about the resource, such as revision histories.