The Arabic Alphabet has 28 letters. The shape of these letters changes depending on their position in the word, whether isolated; in the beginning of the word (initial); in the middle (medial); or at the end (final). http://www.sakkal.com/Arab_Calligraphy_Art1.html
The Arabic alphabet is the Arabic script as it is codified for writing the Arabic language. It is written from right to left, in a cursive style, and includes 28 letters. Because letters usually stand for consonants, it is classified as an abjad. Time period: 400 to the present. Parent systems: Proto-Sinaitic, Phoenician, Aramaic, Syriac, Nabataean.