A pencil tower is a high-rise building or skyscraper with a very high slenderness ratio that is very tall and thin. There is no universal definition of how slender these buildings are to be categorized, but some definitions of 10:1 or 12:1 ratios and higher have been used.

Billionaires' Row is the name of a group of ultra-luxury residential skyscrapers, and the area surrounding them, near the southern end of Central Park in Manhattan, New York City. Several of these buildings are in the supertall category, taller than 1,000 feet (300 m), and are among the tallest buildings in the world. Since most of these pencil towers are on 57th Street, the term can refer to this street, too.