variance

Etymology

From Middle English variance, variaunce, from Old French variance or directly from Anglo-Latin variaunce, veriaunce, wariaunce; all from Latin variantia.

noun

1. The act of varying or the state of being variable.
2. A difference between what is expected and what is observed; deviation.
   Certain other factors were considered to explain the variance from expected figures. All seven aviators smoked. Each considered himself to be in good physical condition, though none found the time to exercise regularly. No aviator was obese. 1973, United States Army Aviation Digest - Volume 19, page 18
   This remains an important tool and relies on simple subtraction to evaluate the difference ( variance ) between a planned result and an actual measurement. 2004, F. L. Harrison, Dennis Lock, Advanced Project Management: A Structured Approach, page 212
   Whenever a patient is recorded as having a variance (V), it is important to return soon afterwards to see if the care intervention has helped. 2012, Penny Howard, Becky Whittaker (nee Chady), Karen Holland, Placement Learning in Cancer & Palliative Care Nursing, page 160
3. The state of differing or being in conflict.
4. An official permit to do something that is ordinarily forbidden by regulations.
5. (law) A discrepancy between two legal documents.
6. (law) A departure from a cause of action originally in a complaint.
7. (statistics) The second central moment in probability.
8. (physics, chemistry, biology) The number of degrees of freedom in a system.
9. (computing, programming) Covariance and contravariance generally.
   Depending on the variance of the type constructor, the subtyping relation of the simple types may be either preserved, reversed, or ignored for the respective complex types.