What 𝑢 means
In standard LaTeX math mode, type u; the math font italicizes it.
That typesets the mathematical style; it does not need to store the separate Unicode character. Use 𝑢 as a character when plain text itself needs to retain the math-italic distinction.
What does math italic u mean?
It marks a variable; its formula supplies the value.
Mathematical italic grew from print conventions. Earlier algebra printed abbreviations in upright type; François Viète used single upright capitals for unknowns in 1591. René Descartes's 1637 book La Géométrie established italic lowercase letters for unknowns and used single letters to name geometric lines.
Unicode's mathematical alphabets extended an earlier, scattered set of letterlike math symbols so plain-text formulas could preserve distinctions carried by letter style. The character 𝑢 therefore has no preset quantity: the author and equation give it a role.
In formulas, the italic style signals a mathematical role; it is not a general-purpose italic font.
Do not replace u inside a word: compatibility normalization can erase the mathematical style.
Don't confuse it with
1Questions people ask
1Does 𝑢 normalize to u?
Yes. Compatibility normalization such as NFKC maps mathematical alphanumeric letters to their base letters, so it can turn 𝑢 into plain `u`. Canonical normalization preserves this distinction.
How to type 𝑢
𝑢\1D462Codes and encoding1 code points
A visible symbol can contain several code points. JS .length counts UTF-16 units; UTF-8 counts bytes.