A mezzanine is an intermediate floor (or floors) in a building which is open to the floor below.
Mezzanines help to make a high-ceiling-ed space feel more personal and less vast, and can create additional floor space.
In industrial settings, mezzanines may be installed (rather than built as part of the structure) in high-ceiling-ed spaces such as warehouses. These semi-permanent structures are usually free-standing, can be dismantled and relocated, and are sold commercially. Industrial mezzanine structures can be supported by structural steel columns and elements, or by racks or shelves.