The Arabic alphabet is a set of characters used to write the Arabic languages, as well as several other unrelated languages in the Middle East and Asia (for example, Farsi). It is based on the Phoenician alphabet, from which the Hebrew and Greek alphabets are also descended. Unlike its sister scripts, the Arabic alphabet is always cursive, and often a letter has several variants depending on its position in a word.
Like Hebrew, Arabic is not a true alphabet, and can more accurately be described as an abjad: that is, a set of characters with no specific symbols for vowels. Instead, diacritical marks (harakat or tashkil) are used to render short vowels, primarily in the Qur'an, and the consonants ʾalif, wāw, and yāʾ are used to render long vowels (similar to matres lectionis in Hebrew). However, which letters and which diacritics are used largely depends on the national variant of the alphabet. The variations used to write some languages have some of the letters adapted to represent vowels; thus, those variations are true alphabets.
The Arabic alphabet, in its basic form, consists of: ʾalif, bāʾ, tāʾ, ṯāʾ, ǧīm, ḥāʾ, ḫāʾ, dāl, ḏāl, rāʾ, zāī, sīn, šīn, ṣād, ḍād, ṭāʾ, ẓāʾ, ʿayn, ġayn, fāʾ, qāf, kāf, lām, mīm, nūn, hāʾ, wāw, and yāʾ.