Standard deviation is a statistical measure that indicates how much individual data points in a set differ from the mean (average) of that set. A low standard deviation means that the data points are close to the mean, while a high standard deviation indicates that the data points are spread out over a wider range of values. To calculate standard deviation, you first find the mean of the data set, then determine the differences between each data point and the mean. These differences are squared, averaged, and finally, the square root of that average gives you the standard deviation.