Glyph is a broad term that refers to any kind of mark that means to convey a message or purpose. It can be a single letter or symbol.

In typography, a glyph is a specific shape or design used to represent a character. Meaning, a glyph can represent a single character in a multitude of ways depending on how its is designed to look.

For example: If you have 9 different designs for the letter ‘a’, you have 9 glyphs.

Glyph - Wikipedia
Source: Wikipedia

A collection of glyphs in the same design family is considered a typeface. A collection of organised glyphs can be used to spell words.