The Collaborative International Dictionary of English v.0.48:

Patio \Pa"ti*o\ (p[aum]"t[-e]*[-o]), n. [Sp., a court] (Metal)
   A paved yard or floor where ores are cleaned and sorted, or
   where ore, salt, mercury, etc., are trampled by horses, to
   effect intermixture and amalgamation.
   [1913 Webster]

   Note: The patio process is used to reduce silver ores by
         amalgamation.
         [1913 Webster]

   2. In Spain, Spanish America, etc., a court or courtyard of a
      house or other building; esp., an inner court open to the
      sky.
      [Webster 1913 Suppl.]

   3. (p[a^]t"[-e]*[=o]`) A usually paved area adjacent to a
      dwelling, used for outdoor lounging, dining, receptions of
      guests, etc.
      [PJC]

WordNet (r) 3.0 (2006):

patio
    n 1: usually paved outdoor area adjoining a residence [syn:
         patio, terrace]