Manhattan is one borough of five, but the other four (the Bronx, Brooklyn, Queens, and Staten Island) are often called the “outer boroughs.” The term “outer boroughs” was used soon after New York’s consolidation in 1898.
 
The term “outer boroughs” is somewhat disparaging, although people in those boroughs still sometimes call a trip to Manhattan as “going to the city.” An abbreviation of “outer borough” is “outerB/outerb.”
   
     
Urban Dictionary 
outer boroughs
Any borough of NYC that is not Manhattan, namely Queens, Brooklyn, Bronx, and Staten Island. Mainly used by Manhattan elitists who do not consider the four other boroughs part of NYC property- but it is.
She lives in one of the outer boroughs and commutes to work.
by Shirley L. New York City Jan 14, 2006
 
16 August 1906, New York (NY) Times, “Interborough Travel,” pg. 6:
No contractor should have a share of the fat of travel of Manhattan unless he would do his share toward developing the outer boroughs.
 
12 November 1910, New York (NY) Times, “Manhattan and the Tri Borough,” pg. 8: 
Manhattan is well disposed to all the outer boroughs, and is anxious only that subways shall be provided capable of dispersing travelers from them quickly and cheaply throughout all sections of the central borough.
 
27 November 1913, New York (NY) Times, “A Question For Every Borough,” pg. 7:
That means not that Manhattan suffers, but that the outer boroughs suffer more than they appreciate.
 
7 October 1920, New York (NY) Times, pg. 10:
THE CITY’S OUTER BOROUGHS.
 
4 November 1984, New York (NY) Times, “Utopia in the Outer Boroughs” by Paul Goldberger, pg. 429:
New Yorkers sometimes say that Middle America begins at the East River, that once you get outside of Manhattan, the rest of New York starts to look, if not quite like other places, a lot more ordinary, a lot more mundane, a lot more like Trenton or Hartford or Erie, Pa., than like the most intense city in the world.
 
Hardly. While it is true that the voltage level drops noticeably in Brooklyn and Queens and the Bronx, and descends to almost nothing in Staten Island, the tranquility is deceptive. The outer boroughs, as they are forever destined to be called (even by their own residents, who persist in describing trips to Manhattan as “going to the city”), are as characteristic of New York, in their way, as the skyscrapers of Madison Avenue.
 
Google Books
Street Smart:
The New York of Lumet, Allen, Scorsese and Lee
by Richard Aloysius Blake
Lexington, KY: University Press of Kentucky
2005
Pg. 3:
The limits on knowing New York “troo and troo” are even more obvious for visitors. Far more New Yorkers live in Brooklyn than in Manhattan (that’s a fact), but relatively few visitors travel across famous bridges or through murky subway tunnels to visit them. Nor do they ordinarily visit Staten Island, Queens, or the Bronx, unless they venture up to Yankee Stadium, which sits on the northern edge of the Harlem River, scarcely beyond the upper reaches of Manhattan. The overwhelming majority of the citizens of the real flesh-and-blood city live in what is condescendingly called the “outer” boroughs, while visitors think New York consists of a few visually recognizable sections of Manhattan.
     
Gotham Gazette
Predicting the Big Stories in 2006
December 19, 2005
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John Avlon, columnist, New York Sun:
Queens Will Be the New Brooklyn. And so will the Bronx and Staten Island - the resurgence of what used to be called the “outer-boroughs” will continue beyond the now-tony confines of Park Slope and Brooklyn Heights.
   
Ankit’s blog: Never Give Up
SOME INTERESTING INFO ON NEW YORK IN DIS ARTICLE
Posted by Ankit in NEVER GIVE UP on May 20, 2007 12:02:00 AM
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The focus of interest for most travelers are the areas in and around Manhattan island. When most people think of New York, they think of Manhattan and in fact, Manhattan is generally referred to as “the city”, while the other four boroughs are typically called “the Outer Boroughs”.