Result of a measurement minus the true value of the measurand. Since a true value cannot be determined, in practice the conventional true value is used.
See also: measurement result
Sources:
Orange Book, 2nd ed., p. 6 (https://media.iupac.org/publications/analytical_compendium/)
PAC, 1994, 66, 595. 'Nomenclature for the presentation of results of chemical analysis (IUPAC Recommendations 1994)' on page 601 (https://doi.org/10.1351/pac199466030595)
VIM (https://www.iso.org/standard/45321.html)