Sigma is the 18th letter of the Greek alphabet, but it’s also a measurement of standard deviation and it’s used in particle physics as a measurement for a discovery.

(Seemingly any discovery in particle physics needs a five-sigma level of certainty. This is the equivalent of tossing a coin and getting the same result more than 20 times in a row, because this is very unlikely (try it), a five-sigma result becomes an accepted discovery. So, basically – particle physics is like tossing a coin.)