Definition of "σ"

(mathematics, statistics) Standard deviation.  examples

(mathematics) Sum of divisors.  examples

(mathematics) Braid group algebra.  examples

(physics, scattering) Cross section.  examples

(linguistics, phonology) Syllable.

(phonology, obsolete) a labialized alveolar fricative (value uncertain, possibly IPA [θʷ]).

(spatial databases) The select operation.  examples

(physics) The Stefan-Boltzmann constant.  examples

(chemistry) A shielding constant.  examples