Glyph
One drawn shape in a font: a letter, a number, a mark or a symbol.
See it in ASCII art. Switch Characters to Braille and see the picture drawn in dot glyphs.
In plain words
A glyph is one drawn shape inside a font. The letter a is a glyph, and so are 7, the question mark and a Braille dot pattern. One letter can have several glyphs, such as a plain a and a fancy a in the same font. A font file is mostly a big set of glyphs plus rules for spacing them. ASCII art treats each glyph as a small block of ink with its own darkness.