x

X is the twenty-fourth letter of the Latin alphabet and is widely used as a symbol in science, mathematics, and culture. Its name in English is pronounced eks; historically, the letter derives from the Greek chi via Latin, though it serves as a general symbol rather than a letter-specific sign in most technical contexts.

In mathematics, X typically represents an unknown value or a variable in equations. In algebra, it can denote a quantity to be solved; in geometry and physics it is used for coordinates (the x-axis) in two-dimensional space. In statistics, X is often used to denote a random variable or observed data.

X has several scientific uses. In biology, the X chromosome is a sex chromosome; in physics and chemistry, X sometimes marks a variable in reaction schemes or is used to denote a generic substituent, such as X in organic chemistry notation. The prefix X-ray denotes high-energy electromagnetic radiation discovered by Wilhelm Röntgen in 1895.

In computing and information technology, the X Window System, or X11, provides a graphical framework for Unix-like operating systems. In popular culture and branding, the term X appears in product names and logos; notably, the social media platform formerly known as Twitter rebranded to X in 2023. X also appears as a Roman numeral for ten and as a generic mark or cross.

Overall, X functions as a versatile placeholder, coordinate, or symbol across diverse fields.