The probability of covering the expected value of an estimated parameter with an interval estimated for the parameter (symbol 1- α). The confidence level can be expressed as a number between 0 and 1, or in percent. The complementary quantity is known as the significance level.
In some cases the confidence level is dictated by the needs of the situation. In all other instances, use of 1- α = 0.95 is recommended.
PAC, 1994, 66, 595. 'Nomenclature for the presentation of results of chemical analysis (IUPAC Recommendations 1994)' on page 599 (https://doi.org/10.1351/pac199466030595)