1. One whose domicile lies at an appreciable distance from his or her place of business.
2. A value far from most others in a set of data: "Outliers make statistical analyses difficult" (Harvey Motulsky).
3. Geology. A portion of stratified rock separated from a main formation by erosion.

The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.