What 𝒬 means
There is no universal object attached to 𝒬. The formula tells you what the author has named with it. Mathematical writing already used styles to keep symbols distinct; a Unicode proposal in 1999 aimed to preserve these differences as text and extend a smaller set of encoded math letters.
Why does script Q look different across math fonts?
Math fonts can choose different script hands. Reference charts show roundhand, a rounded formal style; some math fonts use chancery, a more slanted pen style. Most texts treat them alike, though some authors distinguish the two alphabets. Where supported, U+FE00 requests chancery and U+FE01 roundhand.
Technical notation: the script style can distinguish this mathematical letter from plain Q.
Keep 𝒬 in math or technical notation; use ordinary letters with formatting for everyday words.
Don't confuse it with
1Questions people ask
1Why does 𝒬 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 𝒬
𝒬\1D4ACCodes and encoding1 code points
A visible symbol can contain several code points. JS .length counts UTF-16 units; UTF-8 counts bytes.