In linguistics, a grapheme is the smallest unit of a writing system of any given language.Coulmas, F. (1996), The Blackwell's Encyclopedia of Writing Systems, Oxford: Blackwells, p.174 An individual grapheme may or may not carry meaning by itself, and may or may not correspond to a single phoneme of the spoken language. Graphemes include alphabetic letters, typographic ligatures, Chinese characters, , punctuation marks, and other individual symbols. A grapheme can also be construed as a graphical sign that independently represents a portion of linguistic material.Altmann, G., & Fengxiang, F. (Eds.). (2008). Analyses of script : properties of characters and writing systems
The concept of graphemes is an abstract one and similar to the notion in computing of a character. By comparison, a specific shape that represents any particular grapheme in a specific typeface is called a glyph. For example, the grapheme corresponding to the abstract concept of "the Arabic numeral one" has two distinct glyphs () in the fonts Times New Roman and Helvetica.
For example, in written English (or other languages using the Latin alphabet), there are many different physical representations of the lowercase letter "a", such as a, ɑ, etc. But because the substitution of any of these for any other cannot change the meaning of a word, they are considered to be allographs of the same grapheme, which can be written . Italic and bold face are also allographic.
There is some disagreement as to whether capital and lower-case letters are allographs or distinct graphemes. Capitals are generally found in certain triggering contexts which do not change the word: When used as a proper name, for example, or at the beginning of a sentence, or all caps in a newspaper headline. Some linguists consider digraphs like the in ship to be distinct graphemes, but these are generally analyzed as sequences of graphemes. Ligatures, however, such as , are distinct graphemes, as are various letters with distinctive , such as .
Not all graphemes are phonographic (write sounds). There are additional graphemic components used in writing, such as , mathematical symbols, such as the space, and other typographic symbols. Ancient logogram often used silent to disambiguate the meaning of a neighboring (non-silent) word.
Multigraphs representing a single phoneme are normally treated as combinations of separate letters, not as graphemes in their own right. However, in some languages a multigraph may be treated as a single unit for the purposes of collation; for example, in a Czech language dictionary, the section for words that start with comes after that for . For more examples, see .