Notdef glyph

It is used to visually indicate that a Unicode character has no associated glyph in the current typeface. The notdef glyph is thus displayed instead to signal this absence.{{cite web |last=PeterCon |title=Recommendations for OpenType Fonts (OpenType 1.7) - Typography |url=https://learn.microsoft.com/en-us/typography/opentype/otspec170/recom |website=learn.microsoft.com |date=2022-06-09 |access-date=2024-01-06 |language=en-US}} Moreover, there is no typeface that supports all Unicode characters; therefore, the notdef glyph is unavoidable.{{cite web |title=Missing characters and glyphs |url=https://www.w3.org/International/articles/missing-char-glyph/index.en |website=W3C |access-date=2025-06-22 |language=en}}

One frequent occurrence of the notdef glyph arises in the context of emoji interoperability between operating systems. As emoji support is typically introduced asynchronously across platforms, a character rendered correctly on one system may be unrecognized on another due to a lack of font or system-level integration. For instance, newer emojis are often first implemented on iOS before becoming available on Android, which may result in the display of a fallback glyph, commonly the notdef symbol, on devices that lack the corresponding graphical definition.{{cite web |title=Why are Some Emojis Not Showing Up? Here's How to Fix Those Appearing in Boxes |url=https://www.techtimes.com/articles/251349/20200724/why-emojis-showing-up-heres-fix-those-appearing-boxes-android.htm |website=TechTimes |date=2020-07-24 |access-date=2025-06-22 |language=en}}

File:Notdef glyph variations.svg

The notdef glyph can vary graphically from one font to another. However, despite this variety, it is generally represented in a recognizable way to clearly signal the absence of a specific character. Common examples of frequently observed forms{{refn|group=note|name=commonstyles|This claim lacks a specific source.}} include:

• An outline of a square or rectangle, this basic geometric shape allows quick and clear identification of the notdef glyph;
• An outline of a square, rectangle, or diamond with a question mark in the center, visually emphasizes the uncertain or undefined nature of the missing character;
• An outline of a square or rectangle with a cross in the center, creating a distinctive notdef glyph with a universal connotation of error.

The term "notdef glyph" is composed of two parts:

1. {{lang|en|notdef}}: A contraction of "{{lang|en|not defined}}", meaning "undefined" or "not definable". In the context of fonts, it refers to the absence of a graphical definition for the given character.
2. Glyph: From Ancient Greek, a graphical representation of a character or symbol in a font. A glyph is the basic unit used for text display.

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• Unicode
• Font
• Emoji
• Character encoding
• Typographic symbol

Category:Typographical symbols

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