A diacritic is a mark, usually found above, below, within, or next to a letter or character to distinguish it from the surrounding characters. Its purpose varies with each language. The most common uses of a diacritic or diacritical mark is to denote stress, specify phonetic value, define a sound not in the normal alphabet, or distinguish the entire word from another with the same spelling. There are numerous types of diacritics, but the most common are the acute and grave accent marks as well as the macron.
The acute accent — shown as ´ — is used frequently in Latin-based languages. It marks the stressed vowel in words and also serves to differentiate between homophones in languages like Spanish.
Grave accents — depicted as ` — typically denote the secondary stresses in many words. In some instances, primarily in the English language, it shows stress on a vowel where it is normally not pronounced. It is commonly used in Italian and Catalan to show primary stress.
Macrons — or ¯ — usually show long vowels. Unlike most diacritical accents, macrons may appear above or below the letter. The popularity of macrons is ever changing, and today, in many languages primarily use them in dictionaries.
There are several other instances when a diacritic is used. A diacritic may completely change the sound of a letter such as how a tilde changes the “n” to also incorporate a “y” sound in piña. Apostrophes are occasionally accepted as diacritics, particularly when they denote a missing letter such as in the word “aren’t.” Diaeresis marks are used in some names such as "Chloë," and in many words with double vowels to emphasize separate pronunciations of the vowels.
Diacritics are found in almost every language worldwide, some incorporate them within the alphabet, while others, such as English, only use them when assimilating words from other languages or for poetic purposes. In the Hebrew niquud and the Arabic harakat, the diacritic is used to show sounds that are not in the available alphabet, while the Arabic sukūn utilizes it to show an absence of vowels. Some languages such as Faroese and Icelandic languages use diacritic marks regularly, and they are incorporated in the alphabet. The Greek language uses diacritical marks to show when a letter is being used as a numeral.