grapheme

A fundamental unit of a writing system, corresponding to (for example) letters in the English alphabet or jamo in Korean hangul.

For instance, it is convenient to refer to a single Chinese character as being a grapheme in some contexts.

A sequence of one or more code points that are processed and displayed as a single graphical unit of a writing system.

Even so, it's important for Unicode-friendly applications to deal with text in their user interfaces as a series of graphemes and not as a series of Unicode code points […]

In alphabetic writing, the shortest group of letters composing a phoneme.

The term for a letter or combination of letters which represents a particular sound is a “grapheme”. Languages like Italian and Serbo-Croatian have very simple “grapheme–phoneme conversion” rules.

In terms of specific graphemes, Table 2.5 identifies the most frequent inconsistent phoneme-to-grapheme patterns.