True south is the direction towards the southern end of the axis about which the earth rotates, called the South Pole. The South Pole is located in Antarctica. Magnetic south is the direction towards the south magnetic pole, some distance away from the south geographic pole.
The etymology of "south" can be traced back to the Old English word suth, related to the Old High German word sund, and perhaps sunne in Old English, with sense of "the region of the sun."
Capitalized, this word is used to represent those "regions or countries lying to the south of a specified or implied point of orientation, especially the southeastern part of the United States." (Merriam-Webster Dictionary: http://www-m-w.com).
