I have searched quite a bit, but all I can find is en and em dashes?
I thought Unicode tries to be specific about the use and meaning of a character, so I am expecting something specific.
Is there any such character, or en and em dashes are actually the one used in typesetting mathematics horizontal fraction bar?
Unicode is a character set for mapping between characters/glyphs to numbers. It only deals with plain text and is not supposed for formatting text
Rich Text. Also known as styled text. The result of adding information to plain text. Examples of information that can be added include font data, color, formatting information, phonetic annotations, interlinear text, and so on. The Unicode Standard does not address the representation of rich text. It is expected that systems and applications will implement proprietary forms of rich text. Some public forms of rich text are available (for example, ODA, HTML, and SGML). When everything except primary content is removed from rich text, only plain text should remain.
https://unicode.org/glossary/#rich_text (emphasis mine)
You can't make a letter bold, italic or move a letter to above or below the baseline purely with the Unicode code points (see Create Unicode subscripts and superscripts with combining glyphs). Therefore it has no way to format math expressions either (except for very simple ones). There are a lot of horizontal bars in Unicode, but none can have digits above and below as a single fraction
That means you must use a math rendering tool like LaTeX, MS Equation Editor, MathType, MathML... if you really want fractions with a horizontal bar, because math expressions are just a kind of rich texts. Using pure Unicode you can only have slash fractions. There are some built-in ones like ⅔, ¼, ⅝ and a solidus / or fraction slash ⁄ for arbitrary fractions using numbers in the subscript and superscript blocks: ⁰¹²³⁴⁵⁶⁷⁸⁹₀₁₂₃₄₅₆₇₈₉. For example you can have ⁴⁶⁵/₁₀₈₉ (solidus) or ⁷⁸¹⁵⁄₆₉₂₃ (fraction slash). Many font renderers are smart enough to kern digits before and after U+2044 ⁄ fraction slash as you may see in the previous example
Some more references from the Unicode standard:
Q: What is the difference between “rich text” and “plain text”?
A: Rich text is text with all its formatting information: typeface, point size, weight, kerning, and so on. Plain text is the underlying content stream to which formatting is applied.
One key distinction between the two is that rich text breaks the text up into runs and applies uniform formatting to each run. As such, rich text is inherently stateful. Plain text is not stateful. It should be possible to lose the first half of a block of plain text without any impact on rendering.
Unicode, by design, only deals with plain text. It doesn't provide a generalized solution to rich text issues.
Q: Why doesn't Unicode have a full set of superscripts and subscripts?
A: The superscripted and subscripted characters encoded in Unicode are either compatibility characters encoded for roundtrip conversion of data from legacy standards, or are actually modifier letters used with particular meanings in technical transcriptional systems such as IPA and UPA. Those characters are not intended for general superscripting or subscripting of arbitrary text strings—for such textual effects, you should use text styles or markup in rich text, instead.
