The Collaborative International Dictionary of English v.0.48:

Standard \Stand"ard\, a.
   1. Being, affording, or according with, a standard for
      comparison and judgment; as, standard time; standard
      weights and measures; a standard authority as to nautical
      terms; standard gold or silver.
      [1913 Webster]

   2. Hence: Having a recognized and permanent value; as,
      standard works in history; standard authors.
      [1913 Webster]

   3. (Hort.)
      (a) Not supported by, or fastened to, a wall; as, standard
          fruit trees.
      (b) Not of the dwarf kind; as, a standard pear tree.
          [1913 Webster]

   Standard candle, Standard gauge. See under Candle, and
      Gauge.

   Standard solution. (Chem.) See Standardized solution,
      under Solution.
      [1913 Webster]

WordNet (r) 3.0 (2006):

standard gauge
    n 1: railroad track having the standard width of 56.5 inches