Source : Webster's Revised Unabridged Dictionary (1913)

Mezzanine \Mez"za*nine\, n.
   1. A flooring laid over a floor to bring it up to some height
      or level.

   2. Also

   {mezzanine floor}. (Theat.) A floor under the stage, from
      which various contrivances, as traps, are worked.

Source : WordNet®

mezzanine floor
     n : intermediate floor just above the ground floor [syn: {mezzanine}]