An accent placed over a vowel to indicate that it is of short duration or pronounced differently?

You're describing a diacritic. Diacritics are marks added to letters to change their pronunciation. While the specific meaning of a diacritic can vary depending on the language, there are some common ones that indicate vowel duration:

* Breve (˘) This mark is placed over a vowel to indicate a short pronunciation. For example, in English, the word "cat" has a breve over the "a" because it's pronounced with a short vowel sound.

* Macron (¯) This mark is placed over a vowel to indicate a long pronunciation. For example, in English, the word "fate" has a macron over the "a" because it's pronounced with a long vowel sound.

Here are some other examples:

* Acute accent (´) Often used to indicate a stressed syllable or a change in vowel pronunciation, sometimes indicating a longer duration.

* Grave accent (`) Similar to the acute accent, used to indicate a stressed syllable or a change in vowel pronunciation.

* Circumflex (^) This diacritic can indicate a variety of things, including a change in pronunciation, a stressed syllable, or a vowel that has been lengthened or shortened.

It's important to note that the specific meaning of a diacritic can vary depending on the language and writing system.

If you can provide more context about the language you're interested in, I can give you a more specific answer.