An "Ümlaut" is a diacritical mark used in the German language, consisting of two dots placed over a vowel. It alters the pronunciation of the vowel, typically changing the sound from a back vowel to a front vowel. For example, the letter "a" becomes "ä," "o" becomes "ö," and "u" becomes "ü." This modification can change the meaning of words, making it an essential aspect of German phonetics. The concept of ümlaut also extends to historical linguistics, where it refers to a sound change that occurred in the development of certain languages, including Old English and Old High German. This phenomenon can affect the way vowels are pronounced and can lead to variations in word forms, such as pluralization. Understanding ümlaut is crucial for mastering German pronunciation and grammar.