grapheme

A grapheme is the smallest unit of a writing system that has a specific semantic or phonological value in a language's orthography. It is an abstract representation, while its visible form is called a glyph. Graphemes can be single letters, digraphs, or even entire characters in logographic scripts. The concept helps separate the written form from the sound or meaning it encodes (phonemes, morphemes).

In alphabetic systems like English, graphemes include letters and digraphs such as "a", "e", "th", "sh", "igh", which can correspond to one or more phonemes depending on context. In logographic systems such as Chinese, each character is a grapheme that often encodes a morpheme and syllable rather than a single phoneme. Some scripts use diacritics as separate graphemes or as modifications of base graphemes.

Grapheme-phoneme correspondences vary; some languages have near one-to-one mappings, others have opaque mappings. Graphemes are distinct from phonemes (units of sound) and from glyphs (visible shapes). In digital text, the term grapheme is related to the notion of a grapheme cluster, which is a base character plus combining marks or sequences that form a single user-perceived character.

The term originated in linguistics and is widely used in literacy, typography, and computational linguistics. Understanding graphemes is essential for studying orthography, spellings, and text processing across different writing systems.