What is "grantha alphabet"

The Grantha script ( Tamil Kiranta eḻuttu, Malayalam Grantha lipi) was widely used between the sixth century and the 20th centuries by Tamil speakers in South India, particularly in Tamil Nadu and Kerala, to write Sanskrit and the classical language Manipravalam, and is still in restricted use in traditional Vedic schools ( Sanskrit veda pāṭhaśālā). It is a Brahmic script, having evolved from the Brahmi script in Tamil Nadu. The Malayalam script is a direct descendant of Grantha as are the Tigalari and Sinhala alphabets.

The rising popularity of Devanagari for Sanskrit and the political pressure created by the Tanittamil Iyakkam for its complete replacement by the modern Tamil script led to its gradual disuse and abandonment in Tamil Nadu in the early 20th century, except for specialised Hindu religious literature. Grantha script still lives in Tamil Nadu, albeit in reduced state.