\sigmaThe Greek letter \sigma is commonly used in mathematics and science to represent summation, standard deviation, and other concepts. In mathematics, it is often used to denote the sum of a series. In statistics, it represents the standard deviation of a population. In physics, it can denote surface charge density or cross-sectional area.
Summation notation, where \sigma represents the sum of a series of terms.
\sigma = \sum_{i=1}^{n} x_iStandard deviation formula, where \sigma represents the standard deviation of a population.
\sigma = \sqrt{\frac{1}{N} \sum_{i=1}^{N} (x_i - \mu)^2}Surface charge density, where \sigma represents the charge per unit area.
\sigma = \frac{Q}{A}