Malcolm X). On some identification documents, the letter X represents a non-binary gender, where F means female and M means male. In the Cartesian coordinate system, x is used to refer to the horizontal axis. It is also sometimes used as a typographic approximation for the multiplication sign, . In mathematical typesetting, x meaning an algebraic variable is normally in italic type (), partly to avoid confusion with the multiplication symbol. In fonts containing both x (the letter) and × (the multiplication sign), the two glyphs are dissimilar. It can be used as an abbreviation for 'between' in the context of historical dating; e.g., '1483 x 1485'. Maps and other images sometimes use an X to label a specific location, leading to the expression "X marks the spot". The Roman numeral X represents the number 10. The Suzhou numeral 〤 represents the number 4. In art or fashion, the use of X indicates a collaboration by two or more artists, e.g. Aaron Koblin x Takashi Kawashima. This application, which originated in Japan, now extends to other kinds of collaboration outside the art world. This usage mimics the use of a similar mark in denoting botanical hybrids, for which scientifically the multiplication × is used, but informally a lowercase "x" is also used. At the end of a letter or other correspondence, 'x' can mean a kiss; the earliest example of this usage cited by the Oxford English Dictionary is from 1878. An X rating denotes media such as movies that are intended for adults only. Related characters Descendants and related characters in the Latin alphabet X with diacritics: Ẍ ẍ Ẋ ẋ X̂ x̂ ᶍ IPA-specific symbols related to X: Teuthonista phonetic transcription-specific symbols related to X: ˣ : Modifier letter small x is used for phonetic transcription ₓ : Subscript small x is used in Indo-European studies Ancestors and siblings in other alphabets Χ χ : Greek letter Chi, from which the following derive: Х х : Cyrillic letter Kha : Coptic letter Khe, which derives from Greek Chi : Gothic letter enguz, which derives from Greek Chi 𐌗 : Old Italic X, which derives from Greek Chi, and is the ancestor of modern Latin X : Runic letter Gyfu, which may derive from old Italic X Ξ ξ : Greek letter Xi, which was used in place of Chi in the Eastern (and the modern) Greek alphabets Computing