below stairs

Short definition from Wiktionary

Prepositional phrase

1. 1
   On a floor lower than the one a speaker currently occupies; below the main floor of a multi-floor building.
2. 2
   In or pertaining to the lowest levels of a large house where the house staff work and are accommodated, contrasted with above stairs where the owning family reside.
3. 3
   Common, vulgar.
4. 4
   The areas of a large house in which house staff work, or the staff that work there.

Adjective

1. 1
   Alternative form of below stairs.