Step 1: Understanding the concept of twice born.
In the caste system, the term "twice born" refers to the Brahmin, Kshatriya, and Vaishya castes, as these individuals undergo a sacred initiation ceremony called the "upanayana" and are considered spiritually reborn. This ceremony marks the transition into adulthood and a higher status in society.
Step 2: Explanation of Shudras.
The Shudra caste, in contrast, is not considered twice born and does not undergo the same initiation process as the higher castes. They are traditionally considered the working class, and their role is to serve the other castes.
Step 3: Conclusion.
Thus, the correct answer is Shudra, as this caste is not considered twice born.