In German orthography, the grapheme ß, called Eszett (IPA: [ɛsˈtsɛt]) or scharfes S (IPA: [ˈʃaɐ̯.fəs ˈʔɛs], [ˈʃaː.fəs ˈʔɛs]), in English "sharp S", represents the [s] phoneme in Standard German, specifically when following long vowels and diphthongs, while ss is used after short vowels. The name Eszett represents the German pronunciation of the two letters S and Z.
It originates as the sz digraph as used in Old High German and Middle High German orthography, represented as a ligature of long s and tailed z in blackletter typography (ſʒ), which became conflated with the ligature for long s and round s (ſs) used in Roman type.
The grapheme has an intermediate position between letter and ligature. It behaves as a ligature in that it has no separate position in the alphabet. In alphabetical order it is treated as the equivalent of ⟨ss⟩ (not ⟨sz⟩). It also has no traditional capital form (although some type designers have introduced forms of "capital ß" de facto). It behaves like a letter in that its use is prescribed by orthographical rules and conveys phonological information (use of ß indicates that the preceding vowel is long).