Fictional entities

• X (Dark Horse Comics), a character and its namesake series
• X (Mega Man), protagonist of the Mega Man X video game series
• X (The X-Files), a television series character
• Radio X, the fictional radio station broadcasting the Grand Theft Auto: San Andreas soundtrack
• X, a symbol used on treasure maps in fiction to show the location of the hidden treasure
• See also: X Marks the Spot
• X, a character from the fourth season of Battle for Dream Island, an animated web series
• X Parasite, an element of the 2002 game Metroid Fusion

Film

• X (1963 film), subtitled The Man with the X-Ray Eyes, an American science fiction film
• X (1986 film), a Norwegian drama directed by Oddvar Einarson
• X (1996 film), an anime film directed by Rintaro, based on the X manga by CLAMP
• X (2022 film), an American horror film directed by Ti West
• X the Unknown , a 1956 British science fiction horror film
• X, alternate title for Malcolm X (1992 film), by Spike Lee
• X: Night of Vengeance , a 2011 thriller by Australian director Jon Hewitt
• X: Past Is Present , a 2015 Indian anthology film
• X rating, a designation for adult-only films

Television

• Kamen Rider X , a Japanese series in the Kamen Rider franchise
• Ultraman X , a 2015 Japanese tokusatsu series
• X (TV series), a Japanese anime series based on the X manga by CLAMP
• X, the production code for the 1966 Doctor Who serial The Ark

Video games

• X (1992 video game) a 3D game for the Nintendo Game Boy console
• X (game series), a science fiction space simulator series by Egosoft
• X (Xbox show), an annual trade show hosted by Microsoft

Literature

• X (Cage book), by avant garde composer John Cage
• X (magazine), a quarterly review of literature and the arts
• X (manga), a 1992 Japanese manga by CLAMP
• X (Grafton novel), 2015, by Sue Grafton
• X (young adult novel), 2015, by Ilyasah Shabazz and Kekla Magoon
• X: A Fabulous Child's Story , a 1972 short story and 1978 picture book by Lois Gould
• X: Or, Betty Shabazz v. The Nation, a 2017 play by Marcus Gardley
• The 'X' Documents, a 1974 collection of British reports on German opposition to Hitler based on meetings with Carl Friedrich Goerdeler
• 'X' Stands for Unknown , a 1984 collection of science essays by Isaac Asimov

Music

Roller coasters

• X2 (roller coaster), at Six Flags Magic Mountain, formerly known as X
• The Walking Dead: The Ride in Thorpe Park, England, formerly known as X

In arts and entertainment

• Director X (born 1975), Canadian music video director, also known as X and Little X
• Márcia X (1959–2005), Brazilian performer and visual artist
• Princess X (musician), former stage name of musician Liza Fox (active since 2010)
• DMX (rapper) (1970–2021), American rapper commonly referred to as "X"
• Shaun Ryder (born 1962), English musician also known as X
• Terminator X (born 1966), stage name for American DJ Norman Roberts, who worked with Public Enemy
• XXXTentacion (1998–2018), American rapper commonly referred to as "X"
• X, ring name of wrestler Carl Ouellet (born 1967)

Other people

• X González (born 1999), American gun control activist
• Clyde X (1931–2009), Nation of Islam official
• Khoisan X (1955–2010), political activist
• Laura X (born 1940), feminist historian
• Malcolm X (1925–1965), civil rights activist
• Michael X (1933–1975), activist and criminal
• Xiuhtezcatl Martinez (born 2000), climate activist, often known as "X"
• X, the girl in the X Case, a landmark court case about abortion in Ireland
• X, pseudonymous author of the 1947 Foreign Affairs "X Article", formally titled "The Sources of Soviet Conduct"
• X, surname often assumed by members of the Nation of Islam

Astronomy

• X, signifying a comet of unknown orbit
• Galaxy X (galaxy), a postulated dark galaxy
• Planet X, a hypothesised planet in the outer solar system

Computing

• OS X (pronounced 'OS ten'), former name of the Apple macOS operating system
• X Window System, referred to as X or X11, a client-server display protocol often used in UNIX environments
• X file format, used by DirectX
• X, the mnemonic for the execute instruction on the TI-990 and the TMS9900
• X#, a High-level assembler for the x86 processor architecture as part of the Cosmos operating system

Mathematics

• X, Roman numeral for 10 (number)
• x, an axis in the Cartesian coordinate system
• x, a variable for unknown or changing concepts in mathematics
• A typographical approximation for:
  • Cross product (×)
  • Multiplication sign (× or ✕)

Physics

• X (charge), a conserved quantum number in particle physics
• X band, part of the microwave band of the electromagnetic spectrum
• X unit, unit of length in physics

Other uses in science, technology, and mathematics

• × (or x), used in some types of hybrid names in botany
• X chromosome, a sex determinant in many animal species, including mammals
• X, the pseudoelement symbol for a halogen or halide in organic chemistry