English basement
An English basement is an apartment on the lowest floor of a building, generally a townhouse or brownstone, which is partially below and partially above ground level and which has its own separate entrance from the rest of the building.
Realty
English basements are often rented out separately from the main dwelling, either by a single landlord who owns both portions of the building or by a tenant of the building who sub-lets the English basement. English basements are most common in larger, older cities like London, New York City, Boston, and Washington, D.C..
Phrase
In other cities, such as Chicago and San Francisco, this space is referred to as a "garden apartment". The phrase "English basement" is an Americanism. In the United Kingdom, this style of apartment is known as a "garden flat". The origin of the term "English basement" dates back to at least the mid-19th century. The earliest citation in the OED is 1853 ("1853 N.Y. Daily Times 8 July 5/3 (advt.) House for sale... A new three-story English basement house."). Some people refer to it as the "garden level". Building codes in most cities use neither of the phrases, stating that any floor partly below grade-level is simply a "basement" and a floor more than 50% below grade-level is a "cellar".