nautical mile

Short definition from Wiktionary

Noun

1. 1
   A unit of length corresponding approximately to one minute of arc of latitude along any meridian. By international agreement it is exactly 1,852 metres (approximately 6,076 feet or 1.151 statute mile).
2. 2
   Synonym of sea mile, a historical Scandinavian unit of distance equal to about 4 nmi.