Mezzanines

noun

1. A secondary floor, in between the main floors of a building; entresol.

   "On our way to the top floor, we stopped at the mezzanine."

2. A small window used to light such a secondary floor.
3. The lowest balcony in an auditorium.
4. Additional flooring laid over a floor to bring it up to some height or level.
5. A floor under the stage, from which contrivances such as traps are worked.