The nautical mile is unit of length defined as 1852 meters, which is approximately equal to 6076.115 feet or 1.15078 (statute) miles. It is used in navigation because it is approximately equal to the distance along 1 arcminute of latitude Eric Weisstein's World of Math at the Earth Eric Weisstein's World of Astronomy's equator.
References
Bureau International des Poids et Mesures. "The International System of Units (SI), 7th ed." 1998. http://www1.bipm.org/en/si/si_brochure/.
U.S. Department of Defense. "DOD Dictionary of Military Terms." http://www.dtic.mil/doctrine/jel/doddict/.
