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An estate is a large parcel of land under single ownership, which would historically generate income for its owner.
In the UK, historically an estate comprises the houses, outbuildings, supporting farmland, and woods that surround the gardens and grounds of a very large property, such as a country house, mansion, palace or castle.  It is the modern term for a manor, but lacks a manor's now-abolished jurisdiction.
The "estate" formed an economic system where the profits from its produce and rents (of housing or agricultural land) sustained the main household, formerly known as the manor house. Thus, "the estate" may refer to all other cottages and villages in the same ownership as the mansion itself, covering more than one former manor. Examples of such great estates are Woburn Abbey in Bedfordshire, England, and Blenheim Palace, in Oxfordshire, England, built to replace the former manor house of Woodstock. In a more urban context are the "Great Estates" in Central London such as the Grosvenor and Portman, which continue to generate significant income through rent. 
Before the 1870s, these estates often encompassed several thousand acres, generally consisting of several farms let to tenants; the great house was supplied with food from its own home farm (for meat and dairy) and a kitchen garden (for fruit and vegetables). However the agricultural depression from the 1870s onwards and the decline of servants meant that the large rural estates declined in social and economic significance, and many of the country houses were destroyed.
Large country estates were traditionally found in New York's Long Island, and Westchester County, the Philadelphia Main Line, Maine's Bar Harbor on Mount Desert Island, and other affluent East Coast enclaves; and the San Francisco Bay Area, early Beverly Hills, California, Montecito, California, Santa Barbara, California and other affluent West Coast enclaves. All these regions had strong traditions of large agricultural, grazing, and productive estates modeled on those in Europe. However, by the late 1940s and early 1950s, many of these estates had been demolished and subdivided, in some cases resulting in suburban villages named for the former owners, as in Baxter Estates, New York.
An important distinction between the United States and England is that "American country estates, unlike English ones, rarely, if ever, supported the house."  American estates have always been about "the pleasures of land ownership and the opportunity to enjoy active, outdoor pursuits."  Although some American estates included farms, they were always in support of the larger recreational purpose. 
Today, large houses on lots of at least several acres in size are often referred to as "estates", in a contemporary updating of the word's usage. Most contemporary American estates are not large enough to include significant amounts of self-supporting productive agricultural land, and the money for their improvement and maintenance usually comes from fortunes earned in other economic sectors besides agriculture. They are distinguished from ordinary middle-class American houses by sheer size, as well as their landscaping, gardens, outbuildings, and most importantly, recreational structures (e.g., tennis courts and swimming pools). This usage is the predominant connotation of "estate" in contemporary American English (when not preceded by the word "real"), which is why "industrial estate" sounds like an oxymoron to Americans, as few wealthy persons would deliberately choose to live next to factories.
Traditional American estates include: