The Tropic of Capricorn is one of the five major circles of latitude that mark maps of the Earth. This is the parallel of latitude that runs approximately 23.5 degrees south of the Equator, and is the farthest southern latitude at which the sun can appear directly overhead. Below this line is the Southern Temperate Zone. North of this line are the Tropics.
This line is called the Tropic of Capricorn because about 2000 years ago, when it was named, the sun appeared directly overhead, at this latitude, during the winter solstice, it was entering the zodiac sign of Capricorn. Now, the sun appears in the constellation sagittarius at its southernmost point. The change is due to precession.
Tropic of Capricorn is also the name of a book written by Henry Miller and first published in 1939.