mezzanine

n. [ F. mezzanine, It. mezzanino, fr. mezzano middle, fr. mezzo middle, half. See Mezzo. ] 1. (Arch.) (a) Same as Entresol. (b) A partial story which is not on the same level with the story of the main part of the edifice, as of a back building, where the floors are on a level with landings of the staircase of the main house. [ 1913 Webster ]

2. A flooring laid over a floor to bring it up to some height or level. [ Webster 1913 Suppl. ]

3. Also
mezzanine floor. (Theat.) A floor under the stage, from which various contrivances, as traps, are worked. [ Webster 1913 Suppl. ]

4. The lowest balcony in a theater, or the forward part of the first balcony. [ PJC ]