A green baize door— a simple, ordinary framed door onto which was tacked a green baize cloth, usually with brass tacks—has, since the mid-eighteenth century, represented the dividing line in wealthy households between staff quarters and the family home. 

Examples abound in popular culture, from Upstairs, Downstairs to Downton Abbey to The Grand Budapest Hotel; and in literature—from Jane Austen to Katherine Mansfield to Evelyn Waugh. (Ernest Green, the longtime steward to Princess Elizabeth and the Duke of Edinburgh, titled his 1963 memoir The Green Baize Door.) 

In The Borrowers, Mary Norton’s 1952 fantasy novel for children, a character innocently asks:

Did all old houses have them—to keep out the noise and smells from the kitchen?