WordNet (r) 3.0 (2006):

metadata
    n 1: data about data; "a library catalog is metadata because it
         describes publications"

The Free On-line Dictionary of Computing (30 December 2018):

metadata
metainformation

    /me't*-day`t*/, or combinations of /may'-/ or
   (Commonwealth) /mee'-/; /-dah`t*/ (Or "meta-data") Data about
   data.  In data processing, metadata is definitional data
   that provides information about or documentation of other data
   managed within an application or environment.

   For example, metadata would document data about data
   elements or attributes, (name, size, data type, etc) and
   data about records or data structures (length, fields,
   columns, etc) and data about data (where it is located, how it
   is associated, ownership, etc.).  Metadata may include
   descriptive information about the context, quality and
   condition, or characteristics of the data.

   A collection of metadata, e.g. in a database, is called a
   data dictionary.

   Myers of The Metadata Company claims to have coined the term
   in 1969 though it appears in the book, "Extension of
   programming language concepts" published in 1968, by Philip
   R. Bagley.  Bagley was a pioneer of computer document
   retrieval.  "A survey of extensible programming languages" by
   Solntsseff and Yezerski (Annual Review in Automatic
   Programming, 1974, pp267-307) cites "the notion of 'metadata'
   introduced by Bagley".

   (2010-05-15)