Noun
Stairs in the back part of a house, as distinguished from the front stairs; hence, a private or indirect way.
Source: Webster's dictionaryback-stairs
At the top of the back stairs of Vidal’s Los Angeles house in the Hollywood Hills, where a chairlift had been assembled to transport the wheelchair-bound Vidal between floors, hung a portrait of a blond teenage boy holding a model sailboat. Source: Internet
Hulan hurried inside, walked across the lobby, and climbed the back stairs to her office. Source: Internet