The term 'MARK OVER A LONG VOWEL' is referring to a macron, which is a diacritical mark used in many languages to indicate a long vowel. It is represented by a horizontal line placed above the letter. The macron is used in many languages, including Latin, Greek, and some modern languages such as Hawaiian. It is also used in English to indicate a long vowel sound, such as in the word 'naïve'.