What is "dvija"

Dvija ( Sanskrit: द्विज) means "twice-born". The concept is premised on the belief that a person is first born physically and at a later date is born for a second time spiritually, usually when he undergoes the rite of passage that initiates him into a school for Vedic studies. The term also refers to members of the three varnas in the traditional Hindu social system, or social classes — the Brahmins (priests and teachers), Kshatriyas (warriors), and Vaishyas (merchants) — whose Sanskara of Upanayana initiation was regarded as a second or spiritual birth.

The word Dvija is neither found in any Vedas and Upanishads, nor is it found in any Vedanga literature such as the Shrauta-sutras or Grihya-sutras. The word is almost entirely missing, in any context, from ancient Sanskrit literature composed before the last centuries of the 1st millennium BCE, and it scarcely appears in Dharmasutras literature. Increasing mentions of it appear in Dharmasastras text of mid to late 1st-millennium CE texts. The presence of the word Dvija is a marker that the text is likely a medieval era Indian text.