Source : Webster's Revised Unabridged Dictionary (1913)

Impasto \Im*pas"to\, n. [It. See {Impaste}.] (Paint.)
   The thickness of the layer or body of pigment applied by the
   painter to his canvas with especial reference to the
   juxtaposition of different colors and tints in forming a
   harmonious whole. --Fairholt.

Source : WordNet®

impasto
     n : painting that applies the pigment thickly so that brush or
         palette knife marks are visible