abjad

An abjad is a type of writing system in which the basic characters primarily represent consonants, while vowels are typically omitted or indicated only by diacritics. This contrasts with alphabets, where both consonants and vowels are regularly written, and with syllabaries, where each symbol encodes a syllable. In an abjad, readers usually supply the vowel sounds from context, knowledge of the language, or occasional vowel marks.

Most well-known abjads are Semitic scripts. Arabic and Hebrew are the best-known examples, with other variants such as Syriac, Phoenician, and the scripts used for Persian, Urdu, and other languages that adapted the Arabic script. In everyday writing, short vowels are often left unwritten, while longer vowels or ambiguous words may be clarified with diacritic marks (in Arabic called harakat) or with optional letters in certain contexts, especially in education, religious texts, or linguistic works.

The term abjad derives from the conventional ordering of the Arabic alphabet. It is formed from the initial letters of the first four consonants commonly used to denote the set in traditional ordering: alif, ba, jim, dal. The concept is also used in reference to abjad numerals, a system in which each letter is assigned a numerical value, a practice dating to the broader Semitic tradition and used in manuscript dating and numerology.

In classification, abjads are distinguished from alphabets (with full vowel notation) and from abugidas (where vowels are represented by diacritics or modifications to consonants). Abjads remain widespread in historical and modern contexts for several languages and orthographies.