# Variance

Wikipedia describes variance as follows:

In probability theory and statistics, variance is the expectation of the squared deviation of a random variable from its mean, and it informally measures how far a set of (random) numbers are spread out from their mean.

Variance the square of standard deviation, or rather, standard deviation is the square root of variance. Thus, sometimes variance is written as $$\sigma^2$$ where $$\sigma$$ stands for the standard deviation.