What letter does the Greek letter 'Sigma' represent in English?

The Greek letter 'Sigma' corresponds to the uppercase letter Σ in the Greek alphabet. This letter is used in various contexts in both mathematics and statistics, often representing the sum of a series of values. In mathematical notation, it signifies the summation operation, which is a key concept in many areas of study, including calculus and statistics. In contrast, the other options presented do not correctly represent the Greek letter 'Sigma'; they correspond to different Greek letters such as 'Y' for Upsilon, 'X' for Chi, and 'Ω' for Omega. Understanding the symbols used in mathematics and their origins from the Greek alphabet is essential for grasping advanced concepts in these fields.