Mathematical Bold Capital O 𝐎

Visual Description: The symbol appears as a bold uppercase O with even, heavy strokes. It has rounded edges and a solid interior, giving it a strong, compact look on the page. In math notation, it is used to stand out from regular text and to signify emphasis. It can appear in calculators and editors as a distinct glyph.

Meaning & Usage: The label identifies a stylistic form of the letter O, not a separate symbol. It signals emphasis or differentiation in formulas, matrices, or vectors. In user interfaces, it helps users quickly signpost a bold variable, constant, or label during data entry and comparisons.

Historical Background: The character belongs to a family of mathematical alphanumeric symbols designed to give typographic variety to mathematical writing. Tools and fonts adopted these glyphs to allow consistent boldface in formulas, notes, and documentation. The concept spread with digital typesetting and educational software, encouraging clear visual distinction without altering meaning.

Practical Use: In calculators and equation editors, you can insert this glyph to quickly denote a bold object, such as a vector or a special constant. Use simple UI controls to toggle bold styling, apply it to a selection, or insert it into templates for matrices or sets. It helps readability when comparing values or outlining steps.

See our category page for related symbols.

Look‑alikes: O (U+4F).

Need styled alternatives? Try the Fancy Text tool.