Hamza (ء) is a letter in the Arabic alphabet, representing the glottal stop. Hamza is not one of the 28 "full" letters and owes its existence to historical inconsistencies in the standard writing system. It is derived from the Arabic letter ʿAyn. In the Phoenician and Aramaic alphabets, from which the Arabic alphabet is descended, the glottal stop was expressed by alif, continued by Alif in the Arabic alphabet. However, Alif was used to express both a glottal stop and also a long vowel. In order to indicate that a glottal stop is used, and not a mere vowel, it was added to Alif diacritically. In modern orthography, hamza may also appear on the line, under certain circumstances as though it were a full letter, independent of an Alif. In Unicode it is at the code point U+0621 and named ARABIC LETTER HAMZA.