Upakarma means beginning, which refers to the ritualistic beginning of learning Veda. Besides learning Vedas, on the Upakarma day, Brahmins ritually change their Upanayana thread accompanied by Shrauta rituals. Upakarma is a Vedic ritual still practiced by the Brahmin community.
Those who follow Yajurveda observe the Upakarma on Shravana Purnima day, that is, on the full moon day in Shravan month. Those who follow Rig-Veda observe the Upakarma on Shravana Nakshatra day in Shravana month. Accordingly, the Upakarma day may be different for the followers of Yajurveda and Rig-Veda.
In Tamil Nadu, Upakarma is known as Avani Avittam. For those who perform their first Upakarma, it is called Thalai Avani Avittam. In Andhra Pradesh, Upakarma ritual in Shravana Purnima is known as Jandhyala Purnima.
Since the day of Shravana Purnima coincides with Hayagriva Jayanti, Brahmins choose this day to begin the study of Vedas. Hayagriva Jayanti refers to the birth anniversary of Lord Hayagriva who is believed to be the incarnation of Lord Vishnu. Lord Hayagriva is credited for restoration of all Vedas to Brahma.
Upakarma ritual is meant to offer prayers and express the gratitude to the ancient sages who gave the knowledge of Vedas and revealed sacred Vedic Mantras to humanity. The next day of Upakarma is observed as Gayatri Japam.
The followers of Samaveda observe the Upakarma on Hasta Nakshatra day in Bhadrapada month. The Samaveda Upakarma day usually occurs after a fortnight of Yajurveda and Rig-Veda Upakarma day.