Source : Webster's Revised Unabridged Dictionary (1913)

Relevance \Rel"e*vance\ (r?l"?*vans), Relevancy \Rel"e*van*cy\
   (-van*s?), n.
   1. The quality or state of being relevant; pertinency;
      applicability.

            Its answer little meaning, little relevancy bore.
                                                  --Poe.

   2. (Scots Law) Sufficiency to infer the conclusion.

Source : WordNet®

relevance
     n : the relation of something to the matter at hand [syn: {relevancy}]
         [ant: {irrelevance}]

Source : Free On-Line Dictionary of Computing

relevance
     
         A measure of how closely a given object
        (file, {web page}, database {record}, etc.) matches a user's
        search for information.
     
        The relevance {algorithms} used in most large web {search
        engines} today are based on fairly simple word-occurence
        measurement: if the word "daffodil" occurs on a given page,
        then that page is considered relevant to a {query} on the word
        "daffodil"; and its relevance is quantised as a factor of the
        number of times the word occurs in the page, on whether
        "daffodil" occurs in title of the page or in its META
        keywords, in the first {N} words of the page, in a heading,
        and so on; and similarly for words that a {stemmer} says are
        based on "daffodil".
     
        More elaborate (and resource-expensive) relevance algorithms
        may involve thesaurus (or {synonym ring}) lookup; e.g. it
        might rank a document about narcissuses (but which may not
        mention the word "daffodil" anywhere) as relevant to a query
        on "daffodil", since narcissuses and daffodils are basically
        the same thing.  Ditto for queries on "jail" and "gaol", etc.
     
        More elaborate forms of thesaurus lookup may involve
        multilingual thesauri (e.g. knowing that documents in Japanese
        which mention the Japanese word for "narcissus" are relevant
        to your search on "narcissus"), or may involve thesauri (often
        auto-generated) based not on equivalence of meaning, but on
        word-proximity, such that "bulb" or "bloom" may be in the
        thesaurus entry for "daffodil".
     
        {Word spamming} essentially attempts to falsely increase a web
        page's relevance to certain common searches.
     
        See also {subject index}.
     
        (1997-04-09)