grave accent

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A mark ( ` ) indicating a pronounced e for the sake of meter in the usually nonsyllabic ending -ed in English poetry.
• noun A similar mark used in various languages as an indication of vowel quality or quantity.
• noun A similar mark used, as in transliteration of Chinese, to indicate that a syllable has a falling pitch.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun countable A diacritic mark ( ˋ ) used in many languages to distinguish the pronunciations of vowels.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a mark (`) placed above a vowel to indicate pronunciation