/ˈɡlɪf/ is an element of writing: an individual mark on a written medium that contributes to the meaning of what is written.
For example, in most languages written in any variety of the Latin alphabet the dot on a lower-case "i" is not a glyph because it does not convey any distinction, and an i in which the dot has been accidentally omitted is still likely to be read as an "i". In Turkish, however, it is a glyph because that language has two distinct versions of the letter "i", with and without a dot.
In Japanese syllabaries, a number of the characters are made up of more than one separate mark, but in general these separate marks are not glyphs because they have no meaning by themselves. However, in some cases, additional marks fulfill the role of diacritics, to differentiate distinct characters. Such additional marks constitute glyphs.