From Longman Dictionary of Contemporary Englishstandard deviationˌstandard deviˈation noun [countable]technicalHMS a number in statistics that shows by how much members of a mathematical set can be different from the average setExamples from the Corpusstandard deviation• Mean and standard deviation of normally distributed results are shown; otherwise median and range are given.• The distribution remains normal but the standard deviationdecreases as the squareroot of n, the samplesize.• The standard deviation of the estimate of, B is calculated as follows: therefore, the standarddeviation is:.