Abjad
An abjad is a writing system in which all of the letters are consonants. Although vowels can be added in some abjads as diacritics, they are not needed to write a word correctly. Abjad are commonly written from right to left, rather than left to right, like in other writing systems. Well-known examples of abjads are the Arabic alphabet and the Hebrew alphabet.
History
Abjads were the first phonetic writing systems: made to show only a word's pronunciation (instead of its meaning like ideographs or logograms). They would later inspire the creation of alphabets, such as the Greek alphabet, which have letters for both consonants and vowels.
The earliest known abjad in the world is the Phoenician alphabet. Since in Afro-Asiatic languages, the root meaning of a word is found in its consonants, abjads are widely used in those languages. There are also languages without consonant roots that use abjads, such as Persian and Urdu, both of which use the Arabic alphabet.
