Source : Webster's Revised Unabridged Dictionary (1913)

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.

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

   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.

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

   {Standard solution}. (Chem.) See {Standardized solution},
      under {Solution}.

Source : WordNet®

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