The Collaborative International Dictionary of English v.0.48:

Tartaric \Tar*tar"ic\, a. (Chem.)
   Of or pertaining to tartar; derived from, or resembling,
   tartar.
   [1913 Webster]

   Tartaric acid. (a) An acid widely diffused throughout the
      vegetable kingdom, as in grapes, mountain-ash berries,
      etc., and obtained from tartar as a white crystalline
      substance, C2H2(OH)2.(CO2H)2, having a strong pure acid
      taste. It is used in medicine, in dyeing, calico printing,
      photography, etc., and also as a substitute for lemon
      juice. Called also dextro-tartaric acid.
   (b) By extension, any one of the series of isomeric acids
       (racemic acid, levotartaric acid, inactive tartaric acid)
       of which tartaric acid proper is the type.
       [1913 Webster]

WordNet (r) 3.0 (2006):

tartaric acid
    n 1: an acid found in many fruits; used in soft drinks and
         confectionery and baking powder