The greek letter sigma has many meanings and uses in math.
The uppercase form is written as which looks like a fancy or weird looking letter "E". This form indicates we'll be adding a bunch of items. They can be numbers or algebraic expressions.
The lowercase form is written as which looks like a rotated letter "b" in a way. This lowercase form is often used for population standard deviations in statistics.
There are many other uses for this greek letter, so you'll need to provide more context and information to the question.
Sigma is the eighteenth letter of the Greek alphabet. In the system of Greek numerals, it has a value of 200. In general mathematics, uppercase ∑ is used as an operator for summation. When used at the end of a letter-case word, the final form is used
