Step 1: Understanding the Concept:
The question requires differentiating between a 'Varna' (a broad, theoretical social category) and a 'Jati' (a specific, endogamous community, which is what is commonly meant by 'caste').
Step 2: Detailed Explanation:
- (A) Rajput, (B) Yadav, and (C) Brahmin are all examples of Jatis or clusters of Jatis. They are specific communities into which people are born.
- (D) Shudra is one of the four Varnas in the classical Hindu social hierarchy. It is a very broad theoretical category comprising hundreds of different jatis. Unlike the others, it is not a single, specific community.
Step 3: Final Answer:
Shudra is a Varna, not a specific caste (Jati) in the same sense as the other options.