A diacritic is a mark put above, below, through or on a letter. Some examples of diacritics are an acute accent or a grave accent. The word comes from the Greek word διακριτικός (transl. diakritikós, 'distinguishing'). Usually, it affects the way the word is said (pronounced).

diacritic, a mark near or through an alphabetic character to represent a pronunciation different from that of the unmarked character. Diacritics are often used to represent sounds (whether phonemes or other phonetic units) unavailable in an existing script.