Diacritic marks are symbols added to letters to modify their pronunciation or meaning. Common examples include the acute accent (´) in é and the tilde (˜) in ñ. These marks help distinguish between words that would otherwise be spelled the same but have different meanings or sounds. In various languages, diacritic marks play a crucial role in conveying accurate pronunciation. For instance, in French, the circumflex (ˆ) can indicate a historical letter that has been dropped, while in Vietnamese, diacritics can change the tone of a word entirely.