What 𝓐 means
To distinguish a symbol from other letters in a formula.
In the late twentieth century, the American Mathematical Society found that its TeX (a math typesetting system) publications lacked script and Fraktur (blackletter) alphabets. With Donald Knuth's support, type designer Hermann Zapf designed script and Fraktur math fonts for formulas, not running text. A 1999 proposal argued that style changes mathematical meaning and encoding preserves that distinction in plain text.
Don't confuse it with
2Questions people ask
1Why does 𝓐 show as a box on some devices?
Because that device's fonts have no glyph for it. The character is still correct and still copies correctly — the box is a missing glyph, not a broken character.
How to type 𝓐
Windows (Word)
Alt+XType 1D4D0, then Alt+X to get 𝓐.
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 a”.
Linux
Ctrl+Shift+UType 1d4d0, then Enter or Space.
HTML
𝓐CSS
\1D4D0LaTeX (unicode-math)
Load `unicode-math`, then type `\mbfscrA` in math mode.
Codes and encoding1 code points
HTML decimal
𝓐
HTML hex
𝓐
CSS content
content: "\1D4D0";
Each escape is closed by the next backslash; a trailing space is needed before a literal hex digit.
URL encoded
%F0%9D%93%90
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.