σ
Symbol  Format  Data 

σ  Code Point 
U+03C3 
TeX 
\sigma 

SVG 
The Greek letter (sigma) is used in statistics to represent the standard of a population. It also has various uses in other areas of math and science.
The capital Greek letter Σ (Sigma) is visually very similar to the summation symbol (∑) which is the dedicated symbol in math for the summation operation.