An abugida is a writing system between syllabic and alphabetic scripts. They have sequences of consonants and vowels that are written as a unit, each based on the consonant letter. Vowels must be written down as well, but they are secondary.
Syllables are built up of consonants, each of which has an inherent vowel.
Diacritic symbols are used to change or mute the inherent vowel, and separate vowel letters may be used when vowels occur at the beginning of a syllable or on their own.
That is different from a truly alphabetic script, whose whichvowels and consonants have the same status, and an abjad, whose vowels are left out. Examples of abugidas are Ethiopic and some languages found on the Indian subcontinent. Some forms of shorthand use diacritics for vowels.
The name is derived from the first four letters of the Ge'ez (Ethiopic) alphasyllabary writing system.