Chi (letter)

Chi (uppercase/lowercase Χ χ) is the 22nd letter of the Greek alphabet. It is used to represent the "ch" sound (as in Scottish "loch" or German "Bauch") in Ancient and Modern Greek. In the system of Greek numerals, it has a value of 600. Letters that came from it include the Roman X and Cyrillic Х.
In mathematics, the lowercase formula_1 is used to represent characteristic function, chi-square distribution in statistics and Euler characteristic in geometry.