The Collaborative International Dictionary of English v.0.48:

specification \spec`i*fi*ca"tion\
   (sp[e^]s`[i^]*f[i^]*k[=a]"sh[u^]n), n. [Cf. F.
   sp['e]cification, LL. specificatio.]
   1. The act of specifying or determining by a mark or limit;
      notation of limits.
      [1913 Webster]

            This specification or limitation of the question
            hinders the disputers from wandering away from the
            precise point of inquiry.             --I. Watts.
      [1913 Webster]

   2. The designation of particulars; particular mention; as,
      the specification of a charge against an officer.
      [1913 Webster]

   3. A written statement containing a minute description or
      enumeration of particulars, as of charges against a public
      officer, the terms of a contract, the description of an
      invention, as in a patent; also, a single article, item,
      or particular, an allegation of a specific act, as in a
      charge of official misconduct.
      [1913 Webster]

   4. A detailed listing or description of the required
      properties of some object proposed to be built or bought;
      -- usually used in the plural; as, the building
      specifications require that it withstand an earthquake of
      magnitude 8; the program specifications require an option
      to change the menus.
      [PJC]

WordNet (r) 3.0 (2006):

specification
    n 1: a detailed description of design criteria for a piece of
         work [syn: specification, spec]
    2: naming explicitly
    3: (patent law) a document drawn up by the applicant for a
       patent of invention that provides an explicit and detailed
       description of the nature and use of an invention
    4: a restriction that is insisted upon as a condition for an
       agreement [syn: stipulation, specification]

The Free On-line Dictionary of Computing (19 January 2023):

specification
spec

    (spec) A document describing how some system should
   work.

   (2001-02-06)