An abugida is a segmental writing system in which each letter (basic character) represents a consonant accompanied by a specific vowel; other vowels are indicated by modification of the consonant sign, either by means of diacritics or through a change in the form of the consonant. In some abugidas, the absence of a vowel is indicated overtly. About half the writing systems in the world, including the extensive Brahmic system used for most Indo-Aryan languages, are abugidas.