\sigma
The 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_i
Standard 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}