Final answer:
Diacritical marks are symbols or modifications added to letters to indicate phonetic value, stress, or vowel quality. They are used in various languages to indicate pronunciation or differentiate between words.
Step-by-step explanation:
Diaeresis, apostrophe, and accents are referred to as diacritical marks. Diacritical marks are symbols or modifications added to letters to indicate phonetic value, stress, or vowel quality. They are used in various languages to indicate pronunciation or differentiate between words. For example, in English, the diaeresis is used to indicate that two adjacent vowels should be pronounced separately, as in "coöperate."