Ü (or ü) is a letter not used in English. It is commonly used to represent the sound [y]. Ü started as a u with an e above it. It is heavily used in the Turkic languages, such as Turkish. In German, ü can be replaced by the digraph ue respectively, if it is not available on the keyboard.
Germany and Austria change
Ü is one of the 4 extra letters used in German. It can be replaced by using the digraph ue. In English language newspapers, ü is often written as "u", but this is not correct.
Internet addresses are often written as "ue".
German is one of the official languages of Switzerland. Its people who speak German normally use ü.