Between conception and cremation, a Hindu was to have his lifespan punctuated by a total of 16 major samskaras (‘rites of passage’ or ‘initiation ceremonies’) out of which the upanayana samskara is one of the few that still survive in practice. It was primarily meant as an enabler for the study of the Vedas and performance of Vedic sacrifices. Therefore, it is available only to male members from the first three tiers of classical Hindu society, namely, Brahmins, Kshatriyas, and Vaishyas, who can be approximately (if somewhat inaccurately) understood as the intellector class, the warrior class, and the mercantile class respectively. However, there are clear statements in Hindu religious literature to the effect that ‘in earlier times’, the initiation was extended to females also from these classes, and there are hints pointing to the ceremony being inclusive enough to cover members from the fourth class as well. However, it is unambiguous that males from the first three classes are entitled to upanayana. It is the ‘second birth’, which makes them dvi-ja, that is, ‘twice-born’.
The rite enjoins the wearing of a ceremonial string, named the yajnopaveeta (janeu in Hindi). Since it was available only to ‘upper-caste’ Hindus, it also became a desirable symbol and many Hindus would wear it—regardless of the classically given entitlement—in order to demonstrate that they belonged to a ‘high caste’. In particular, it came to be adopted in many caste-based ‘reform movements’ that came up in the late nineteenth and early twentieth centuries. Before that, however, it seems that the non-Brahmins stopped being particular about wearing it long ago in history and the association of the yajnopaveeta with the Brahmin had grown to be nearly exclusive.