This document provides an overview of variance and standard deviation. It defines variance as the average squared deviation from the mean of a data set, and is used to calculate standard deviation. Standard deviation measures how dispersed the data is from the mean - the higher the standard deviation, the more spread out the data. It gives the formulas for calculating variance using summation notation, and standard deviation as the square root of variance. An example is shown finding the variance and standard deviation of 5 test scores.