Standard deviation is a measure of the amount of variation or dispersion of a set of values in statistics. It tells you how much your data scatters around the mean. A low standard deviation indicates that the values tend to be close to the mean of the set, while a high standard deviation indicates that the values are spread out over a wider range. Standard deviation may be abbreviated SD, and is most commonly represented in mathematical texts and equations by the lower case Greek letter σ (sigma), for the population standard deviation, or the Latin letter s, for the sample standard deviation.

To calculate the standard deviation, you can use the following formula:

• Subtract the mean from each data point
• Square the value before adding them all together
• Divide by the total number of data points
• Finally, take the square root to reach the standard deviation of the data

Standard deviation is widely used in experimental and industrial settings to test models against real-world data. It is also used in finance to measure the associated risk in price fluctuations of some asset or portfolio.