X

Roman numeral ten; a person or thing unknown.

x

In mathematics, an unknown quantity.

X

24th letter of the English alphabet, with a sound that is /ks/ medially and /z/ initially. It is derived through Latin from the alphabet of western Greece, and was the last letter in the earlier Latin alphabet.

It did not exist in the North Semitic alphabet. The Ionic alphabet, which later became the classical Greek alphabet, had the letter xei, with the sound /ks/. According to some scholars, however, it did not have the sound /ks/, but was a guttural aspirate, equivalent to the Scottish ch.

x

In computing, wild card character often used to describe versions of hardware or software. One might, therefore, refer to Windows 3.x (any version of Windows, from 3.0 to 3.31), or an x86 chip (any of the chips manufactured by Intel with serial numbers ending in 86).