Ab is the second letter of the Mandaic alphabet and writes b. It joins on both sides, taking initial, medial, final and isolated shapes according to where it falls in a connected run, so it never forces a break in a word.
Its name follows the pattern that runs through most of the alphabet, in which a letter is called by its own sound with the vowel a in front of it. Ab, ag, ad and ah name the second, third, fourth and fifth signs on exactly that plan. These names do not continue the Northwest Semitic nouns that Hebrew and Syriac kept, where the second letter is still called a house, so a Mandaic letter name is usually a way of pronouncing the letter rather than a word carrying a sense of its own.
Ab stands at the second place, which is the place b holds in Hebrew, in Syriac and in the older Aramaic sequence. The first twenty-two Mandaic letters keep that order without alteration, and only the signs added at the end depart from it.
Its sound is not divided into a hard and a soft reading the way Syriac beth is. Mandaic has an affrication mark, written under a letter, that extends the alphabet to sounds the language did not originally have, and it is used with several letters, but the plain and spirantized pair that governs six Syriac letters is not a feature of the Mandaic system.