Sigma

From Wikinfo

1. Sigma (upper case Σ, lower case σ, alternative ς) is a the Greek alphabet. See Sigma (letter).
2. The upper-case letter Σ is used as a symbol for the summation operator forming a series in mathematics.
3. The upper-case letter Σ is used as a symbol for a certain alphabet of a language, or of some other object dependent on an alphabet; expressed in mathematical terms, eg "the language defined by alphabet Σ={a,b,c} and the rules ..."
4. The lower-case letter σ is used as a symbol for the standard deviation of a population in statistics.
5. The lower-case letter σ is used as a symbol for the divisor function in number theory.
6. The lower-case letter σ is used as a symbol for the Stefan-Boltzmann constant of radiation in physics.

References

• Adapted from the Wikipedia article, "Sigma" http://en.wikipedia.org/wiki/Sigma, used under the GNU Free Documentation License