Alif is the first of the twenty-eight letters of the Arabic script and the simplest in form, a single vertical stroke drawn from the top down. It belongs to the small group of six letters that join only to the right, which means a word containing alif is written as two or more separate connected groups rather than one continuous line. That is not a defect of the script but part of its rhythm, and a calligrapher uses the break an alif creates to set the proportions of a whole line. In the classical system of proportional writing associated with the Abbasid vizier Ibn Muqla, the height of the alif is the unit against which every other letter is measured, and the rhombic mark left by the flat of the pen nib is the unit that measures the alif.
Alif is not a consonant in the way ba or mim are. It writes the long vowel a, and it also acts as the seat for the glottal stop, hamza, which is placed above or below it at the beginning of a word. That double duty makes alif the most frequent letter in written Arabic and the one whose spelling is most argued over, since the rules governing whether a hamza sits on an alif, on a waw, on a ya, or on the line by itself are the hardest part of Arabic orthography.
In the abjad reckoning, in which the letters double as numerals, alif carries the value one. Its name descends from the Northwest Semitic aleph, a word meaning ox, but the sense did not travel with the name. To a reader of Arabic, alif is simply what the letter is called.