accent mark

n. diacritical mark, mark placed above or below a letter to show how it is to be pronounced (used in Arabic, Spanish, etc.)

A diacritical mark or diacritic, also called an accent, is a small sign added to a letter to alter pronunciation or to distinguish between similar words. The term derives from Greek διακριτικός (diakritikos, "distinguishing"). "Diacritic" is both adjective and noun, whereas "diacritical" is only an adjective.
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Noun
1. a diacritical mark used to indicate stress or placed above a vowel to indicate a special pronunciation
(synonym) accent
(hypernym) diacritical mark, diacritic
(hyponym) stress mark
(classification) language, linguistic communication