Glyph

A glyph is the drawn shape of a character: the specific marks a font puts on the page. The character is the meaning, the glyph is the picture of it.

The distinction sounds academic and is the root of a whole class of PDF problems. A PDF page does not store the letter "A"; it stores an instruction to draw glyph number 36 from an embedded font. Only a separate mapping inside the file connects that glyph back to the Unicode character it represents. When the mapping is missing or wrong, the page still looks perfect while the text underneath is unreadable to software - copying it produces nonsense, and a screen reader has nothing to say.

One character can also have several glyphs (a normal "a" and a swash "a"), and one glyph can stand for several characters (the "fi" ligature), which is why the mapping has to be recorded rather than inferred from appearance.

Learn more

• Glyphs and characters (Unicode Standard) - the Unicode Consortium on the character/glyph distinction
• Unicode
• Machine-readable text