Noun
A writing system for Arabic, historically also employed as a numeral system, in which there is one glyph (symbol or letter) for each consonant but vowels are not specified.
(linguistics) Any writing system in which glyphs are used to represent consonants or consonantal phonemes, but not vowels.
Languages that use abjads include Arabic, Hebrew, Persian, and Urdu. Abjads differ from syllabaries (such as the Japanese hiragana) in that the vowel quality of each letter is left unspecified, and must be inferred from context and grammar.
The system of abjad numerals; a numeral system in which the letters of the Arabic abjad are interpreted as numerals, typically used to enumerate lists and nested lists, as well as in numerology.
Source: en.wiktionary.orgAbjads and the structure of Semitic languages The abjad form of writing is well-adapted to the morphological structure of the Semitic languages it was developed to write. Source: Internet
Because of this, it is more exactly called an "impure abjad". Source: Internet
The Book Pahlavi script, an abjad, had only twelve letters at one point, and may have had even fewer later on. Source: Internet
Other languages may use a Semitic abjad with mandatory vowel diacritics, effectively making them abugidas. Source: Internet
The Libyco-Berber script was a pure abjad : it had no vowels. Source: Internet