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A glyph is a visual form used to display written content. A text character is the encoded abstract item; a glyph is the shape chosen for its presentation. One text character can have several glyphs, such as contextual forms in Arabic, while several text characters can be displayed by one typographic ligature.

For example, the two text characters “f” and “i” may be drawn separately or replaced by an “fi” typographic ligature. The underlying text can remain the same in both cases. A glyph index identifies a form within a particular computer font; it is not a portable Unicode code point.^[ref]

Typography concerns the selection and arrangement of written forms. In digital systems, the visible result depends on several distinct operations: interpreting text characters, selecting glyphs from a computer font, positioning them, and converting their geometry into pixels through rasterization.

This distinction matters when a document looks wrong. Missing glyphs, incorrect glyph substitutions and poorly rendered pixels can produce different failures even when the underlying Unicode text is unchanged.^[ref]