What is «standard deviation»?

The standard deviation is a measure of how spread out numbers are.
Its symbol is σ (the Greekletter sigma)
The formula is easy: it is the square root of the variance.

mathsisfun.com/data/standard-deviation.html

  • A low standard deviation indicates that the data points tend to be close to the mean (also called the expected value) of the set.
  • A high standard deviation indicates that the data points are spread out over a wider range of values.

The standard deviation is commonly used to measure confidence in statistical conclusions.

en.wikipedia.org/wiki/Standard_deviation