An abjad is a type of writing system where each symbol always or usually stands for a consonant, leaving the reader to supply the appropriate vowel. It is a term suggested by Peter T. Daniels to replace the common terms "consonantary", "consonantal alphabet" or "syllabary" to refer to the family of scripts called West Semitic. In popular usage, abjads often contain the word "alphabet" in their names, such as "Arabic alphabet" and "Phoenician alphabet". The name "abjad" is derived from the Arabic word for alphabet. The word "alphabet" in English has a source in Greek language in which the first two letters were "A" (alpha) and "B" (beta), hence "alphabeta". In Arabic, "A" (ʾAlif), "B" (Bāʾ), "Ǧ" (Ǧīm), "D" (Dāl) make the word "abjad" which means "alphabet". It is also used to enumerate a list in the same manner that "a, b, c, d" (etc.) are used in the English language.

The name "abjad" (ʾabǧad أبجد) is derived from pronouncing the first letters of the Arabic alphabet in order. The ordering (ʾabǧadī ) of Arabic letters used to match that of the older Hebrew, Phoenician and Semitic alphabets; ʾ b g d (read from right to left: أ ب ج د) or أبجد.