What 𝐬 means
In Word, type 1D42C and press Alt+X.
If hexadecimal digits immediately precede the code, select only 1D42C before pressing Alt+X; otherwise Word may convert those extra digits too.
What does bold s mean in an equation?
It is a mathematical letter whose bold style can carry meaning.
Bold type already distinguished symbols in printed mathematics. A 1999 Unicode proposal described these math alphabets as routine in mathematical and technical writing; separate characters let plain-text formulas preserve those distinctions.
Some notation uses bold letters for vectors; other styles use bold italics. This upright 𝐬 alone does not tell you that s is a vector: the formula and its author’s notation do.
Don't confuse it with
4Questions people ask
2Why does 𝐬 appear as a box?
The font used to display the text may lack this mathematical letter, leaving a blank or box. A font that supports mathematical alphabets can supply the glyph.
Will normalization keep 𝐬 bold?
No. Compatibility normalization (NFKC or NFKD) maps it to Latin `s`, removing the bold mathematical distinction; those forms should not be used for mathematical text.
How to type 𝐬
𝐬\1D42CCodes and encoding1 code points
A visible symbol can contain several code points. JS .length counts UTF-16 units; UTF-8 counts bytes.