There are 14 moon letters in the Arabic alphabet. Moon letters are a group of letters in Arabic that change their pronunciation when they come after the definite article "Al". The 14 moon letters are: ت, ث, د, ذ, ر, ز, س, ش, ص, ض, ط, ظ, ل, ن. These letters have a softer pronunciation when they come after "Al".