What is "double acute accent"

n. A rare diacritic mark made up of two acute accents on the same letter, usually a vowel.

The double acute accent ( ˝ ) is a diacritic mark of the Latin script. It is used primarily in written Hungarian, and consequently is sometimes referred to by typographers as Hungarumlaut. The signs formed with diacritic marks are letters in their own right in the Hungarian alphabet (for instance, they are separate letters for the purpose of collation).