Standard deviation
Standard deviation is a measure of how spread out a dataset is. A low standard deviation means most values in the group are close to the mean, while a high standard deviation means the values are spread out over a wide range. For example, the age of students in the same class would have a small standard deviation, as most students would be around the same age as the mean. On the other hand, the age of all students in a school would have a larger standard deviation because the ages would be spread out from 4 to 19 years old. The square of standard deviation is called variance.
See also: distribution, normal distribution, variance