An abugida – sometimes also called alphasyllabary, neosyllabary, or pseudo-alphabet – is a segmental writing system in which consonant–vowel sequences are written as units; each unit is based on a consonant letter, and vowel notation is secondary, similar to a diacritical mark. This contrasts with a full alphabet, in which vowels have status equal to consonants, and with an abjad, in which vowel marking is absent, partial, or optional – in less formal contexts, all three types of the script may be termed "alphabets". The terms also contrast them with a syllabary, in which a single symbol denotes the combination of one consonant and one vowel.

A diacritic is a glyph added to a letter or to a basic glyph. The term derives from the Ancient Greek διακριτικός, from διακρίνω. The word diacritic is a noun, though it is sometimes used in an attributive sense, whereas diacritical is only an adjective. Some diacritics, such as the acute ⟨á⟩, grave ⟨à⟩, and circumflex ⟨â⟩, are often called accents. Diacritics may appear above or below a letter or in some other position such as within the letter or between two letters.