Which Greek letter is represented by the character 'Σ'?

The character 'Σ' represents the Greek letter Sigma. In the Greek alphabet, Sigma corresponds to the English letter 'S.' It is commonly used in various mathematical and scientific contexts, such as representing summation in mathematics, where it signifies the operation of adding a series of numbers. Understanding Greek letters is important in many disciplines, including mathematics, physics, and even in the context of Greek life in fraternities and sororities where these letters often represent chapter names or organizations. The letter Sigma is distinguished from the others listed, as Delta corresponds to 'D,' Upsilon to 'Y,' and Theta to 'Th,' confirming Sigma as the correct answer in this context.