Key Points The X-bar is the sample mean of a given data set. ... In statistics, the Latin small letter x is used to represent a variable in a set of sample data.

Because it’s been employed in so many fields—from algebra, to genetics, to aerospace, to sex and spirituality—X's many meanings make it the most mystifying letter of the alphabet.

Billionaire Elon Musk's decision to rebrand Twitter as X could be complicated legally: companies including Meta and Microsoft already have intellectual property rights to the same letter.

In a paper by Lord Viscount Brouncker in the Philosophical Transactions (vol. ii., 1668, p. 646), the capital letter X occurs regularly as the symbol for multiplication.