Source : Free On-Line Dictionary of Computing

topic map
     
         A collection of "topics", their relationships, and
        information sources.  A topic map captures the subjects of
        which information sources speak, and the relationships between
        them, in a way that is implementation independent.
     
        A topic is a symbol within the computer that represents
        something in the world such as the play Hamlet, the playwright
        William Shakespeare, or the "authorship" relationship.
     
        Topics can have names.  They can also have occurrences, that
        is, information resources that are considered to be relevant
        in some way to their subject.  Topics can play roles in
        relationships.
     
        Thus, topics have three kinds of characteristics: names,
        sources, and roles played in relationships.  The assignment of
        such characteristics is considered to be valid within a
        certain scope, or context.
     
        Topic maps can be merged.  Merging can take place at the
        discretion of the user or application (at runtime), or may be
        indicated by the topic map's author at the time of its
        creation.
     
        (2003-07-19)