Sigma (letter)

Sigma (Σ σ ς) is the 18th letter of the Greek alphabet and has a numeric value of 200. When used at the end of a word, the final form (ς) is used.

The upper-case letter Σ is used as a symbol for:

• summation
• a certain alphabet, of a language, or someother object dependent on an alphabet; expressed in mathematical terms, eg "the language defined by alphabet Σ={a,b,c} and the rules ..."

The lower-case letter σ is used as a symbol for:

• standard deviation
• sigma function

See also:

• Alpha - Beta - Gamma - Delta - Epsilon - Digamma - Zeta - Eta - Theta - Iota - Kappa - Lambda - Mu - Nu - Xi - Omicron - Pi - San - Qoppa - Rho - Sigma - Tau - Upsilon - Phi - Chi - Psi - Omega - Sampi