Umlaut is a name for the two dots diacritical mark as used to indicate in writing the result of the historical sound shift due to which former back vowels are now pronounced as front vowels.

A diacritic is a glyph added to a letter or to a basic glyph. The term derives from the Ancient Greek διακριτικός, from διακρίνω. The word diacritic is a noun, though it is sometimes used in an attributive sense, whereas diacritical is only an adjective. Some diacritics, such as the acute ⟨á⟩, grave ⟨à⟩, and circumflex ⟨â⟩, are often called accents. Diacritics may appear above or below a letter or in some other position such as within the letter or between two letters.