The Brahmanas, Kshatriyas and Vaishyas, who were entitled to the sacred thread ceremony, were collectively called:

The members of the three upper varnas, Brahmanas, Kshatriyas and Vaishyas, were collectively called "dvija", meaning "twice-born".

Why "twice-born"?

The first birth was the physical birth.

The second birth was a spiritual birth, through the ceremony of initiation with the sacred thread, after which a boy could study the Vedas.

Only boys of the three upper varnas were allowed to undergo this initiation, according to the later Vedic texts and the Dharmashastras.

The Shudras and women were generally excluded from this ceremony and from Vedic study.

The varna system in the later Vedic period:

• "Brahmanas": priests and teachers; they performed sacrifices and studied the Vedas.
• "Kshatriyas": rulers and warriors; they protected people and administered justice.
• "Vaishyas": farmers, herders and traders; they paid taxes.
• "Shudras": servants of the three higher varnas; they had the fewest rights.
• The first three varnas had certain rights, such as wearing the sacred thread, studying the Vedas and performing sacrifices.
• The varna system became more rigid in the later Vedic period, and occupations tended to become hereditary.

Other terms:

• "Antyaja": a term used in later texts for those considered outside the four varnas, regarded as "untouchable".
• "Vratya": a person who had not undergone the proper rites, or groups outside the Vedic fold; the Atharvaveda has a section on the Vratyas.
• "Varna" originally meant colour, and later came to mean social order.
• "Jati" refers to birth-based groups (castes), which became more numerous later.

The word "dvija" in other meanings:

It is also used for birds (which are "born twice": first as an egg, then from the egg) and for teeth (milk teeth and permanent teeth).

Why not the other options?

• ✗The Shudras were not counted among the twice-born.
• ✗"Antyaja" referred to groups treated as outside the varna order.
• ✗"Vratya" referred to those who had not undergone the rites.