What 𝓧 means
It can distinguish one mathematical symbol from another.
Unicode, the text standard, extended an earlier scattered set of math symbols made from letters into complete style alphabets. Descartes’s Géométrie, a geometry book from 1637, helped establish plain x, y, and z as letters for unknowns; that history does not make 𝓧 mean “unknown.”
Don't confuse it with
1Questions people ask
1Can software change 𝓧 into plain X?
Yes. Unicode’s NFKC normalization, a text-standardizing process, turns 𝓧 into X and drops the style if a program applies it.
How to type 𝓧
Windows (Word)
Alt+XType 1D4E7, then Alt+X to get 𝓧.
Windows
Win+Rrun charmap for the full table, or use the emoji picker's Ω symbols tab (Win + .).
macOS
Control+Command+SpaceOpen the character viewer and search “mathematical bold script capital x”.
Linux
Ctrl+Shift+UType 1d4e7, then Enter or Space.
HTML
𝓧CSS
\1D4E7HTML source
Write `𝓧` as a numeric character reference; HTML reads it as 𝓧.
Codes and encoding1 code points
HTML decimal
𝓧
HTML hex
𝓧
CSS content
content: "\1D4E7";
Each escape is closed by the next backslash; a trailing space is needed before a literal hex digit.
URL encoded
%F0%9D%93%A7
1
On screen
1
Code points
2
JS .length
4
UTF-8 bytes
A visible symbol can contain several code points. JS .length counts UTF-16 units; UTF-8 counts bytes.