Glyphs are units of visual rendering.
A set of glyphs makes up a font.
Glyphs can be construed as the basic units of organization of the visual rendering of text, just as characters are the basic unit of organization of encoded text.
Glyphs are defined by ISO/IEC 9541-1 as “a recognizable abstract graphic symbol which is independent of a specific design”.
There is not a one-to-one correspondence between characters and glyphs: