outlier

Short definition from Wiktionary

Noun

1. 1
   A person or thing situated away from the main body or outside its proper place.
2. 2
   An exception.
3. 3
   A part of a formation separated from the rest of the formation by erosion.
4. 4
   A value in a statistical sample which does not fit a pattern that describes most other data points; specifically, a value that lies 1.5 IQR beyond the upper or lower quartile.