Definition - What does Upanayana mean?
Upanayana is a traditional Hindu rite of passage (samskara) that usually marks a boy's acceptance into the life of a spiritual student and as a member of the religious community, although the ritual varies by tradition. The term comes from the Sanskrit, upanaya, meaning “initiation” or “obtainment,” and ayana, meaning “arrival,” “way” or “progress.”
During the upanayana ceremony, the young initiate receives the yajnopavita, or sacred thread, which he wears across his chest from the left shoulder to the waist.
Yogapedia explains Upanayana
In very early Vedic texts, all believers were welcome to be initiated, including the lowest classes and women. Traditionally, though, upanayana was limited to the three upper classes of society, but in practice today, the ritual is mostly performed for orthodox Hindus and mostly members of the Brahmin caste, which includes priests, gurus and teachers. Less commonly, upanayana is performed for girls. The age of upanayana varies widely, from five to 24 years old.
While in some regions of India upanayana is associated with adolescence, in the north it may also be performed prior to a wedding ceremony.
Finally, a similar upanayana is performed in the Buddhist tradition as a rite of passage.