Terminology Focus
Uncertainty (of measurement)

Uncertainty (of measurement) is used widely in many different ways, and is always defined in reference to its context.  Even in the very narrow field of metrology, the term is used in different ways in different fields of testing and calibration.  The approved GUM (Guide to the Expression of Uncertainty in Measurement: 1995) definition is:  "uncertainty (of measurement): parameter, associated with the result of a measurement, that characterizes the dispersion of the values that could reasonably be attributed to the measurand."

The preferred use of this term is “uncertainty of measurement,” which can be shortened to “uncertainty,” but only if “of measurement” is understood within the context of its use.  Alternatively, the phrase “measurement uncertainty” may be used.  However, the expression “measurement of uncertainty” should not be used, because uncertainty cannot be “measured”; it can only be estimated.

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