A grapheme is the smallest semantically distinguishing unit in a written language, analogous to the phonemes of spoken languages. A grapheme may or may not carry meaning by itself, and may or may not correspond to a single phoneme. Graphemes include alphabetic letters, typographic ligatures, Chinese characters, numerical digits, punctuation marks, and other individual symbols of any of the world's writing systems.
The word grapheme is derived from Greek γράφω gráphō ("write"), and the suffix -eme, by analogy with phoneme and other names of emic units. The study of graphemes is called graphemics.
Read more about Grapheme: Notation, Glyphs and Allographs, Types of Graphemes, Correspondence Between Graphemes and Phonemes