Arabic letters are the characters used in the Arabic script, which is written from right to left. The alphabet consists of 28 letters, each representing a consonant sound. Vowel sounds are indicated using diacritics, which are small marks placed above or below the letters. Each letter can take different forms depending on its position in a word: initial, medial, final, or isolated. This means that the shape of a letter changes when it is at the beginning, middle, or end of a word, making the script unique and visually distinct from other writing systems.