What ⍰ means
⍰ is the apl functional symbol quad question. Unicode classifies it as an “other symbol” — Unicode's shelf for signs that are neither maths, money nor punctuation and files it in the Miscellaneous Technical block; this site shelves it under Maths.
Its appearance depends on the font and text styling.
How it is encoded
⍰ is a single code point, U+2370. In HTML that is ⍰, and in CSS \2370.
Don't confuse it with
4⌷⌸⌹⌺
APL Functional Symbol Squish Quad
shares “apl”, “functional”, “quad”, “symbol”
APL Functional Symbol Quad Equal
shares “apl”, “functional”, “quad”, “symbol”
APL Functional Symbol Quad Divide
shares “apl”, “functional”, “quad”, “symbol”
APL Functional Symbol Quad Diamond
shares “apl”, “functional”, “quad”, “symbol”
Questions people ask
1Why does ⍰ 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 ⍰
Windows (Word)
Alt+XType 2370, then Alt+X to get ⍰.
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 “apl functional symbol quad question”.
Linux
Ctrl+Shift+UType 2370, then Enter or Space.
HTML
⍰CSS
\2370Codes and encoding1 code points
HTML decimal
⍰
HTML hex
⍰
CSS content
content: "\2370";
Each escape is closed by the next backslash; a trailing space is needed before a literal hex digit.
URL encoded
%E2%8D%B0
1
On screen
1
Code points
1
JS .length
3
UTF-8 bytes
A visible symbol can contain several code points. JS .length counts UTF-16 units; UTF-8 counts bytes.