What 𝐨 means
Use a Unicode hex-input method supported by your app.
In Word for Windows, type 1D428 and press Alt+X. In GNOME on Linux, press Ctrl+Shift+U, type 1d428, then press Enter. As of 2026, macOS Unicode Hex Input accepts only four-digit codes; use Character Viewer for this five-digit code.
What does 𝐨 mean in a formula?
It marks lowercase o in bold; the formula supplies its meaning.
Bold lowercase letters often stand for vectors in physics and applied mathematics, but notation varies by field and author. This character has no universal definition: follow the equation or its stated conventions. Unicode 3.1 (2001) expanded a smaller set of earlier letterlike mathematical forms into a fuller alphabet. These characters were encoded so mathematical style distinctions could survive in plain text; they are meant for mathematical and technical notation.
Why can 𝐨 turn into plain o?
NFKC compatibility normalization can fold it to plain o.
Unicode gives mathematical alphabets compatibility mappings to their base letters. NFKC, a Unicode normalization form, applies those mappings: 𝐨 becomes plain o. This can happen when software normalizes text; it is not just a different font rendering.
Don't confuse it with
4Questions people ask
1Why does 𝐨 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 𝐨
𝐨\1D428Codes and encoding1 code points
A visible symbol can contain several code points. JS .length counts UTF-16 units; UTF-8 counts bytes.