Which group is NOT part of the Hindu caste system?

The group that is not part of the Hindu caste system is indeed the Knights. The Hindu caste system comprises four primary categories: Brahmins (the priestly class), Kshatriyas (the warrior and ruling class), Vaishyas (the merchant and landowner class), and Shudras (the laborer and service class).

Knights, on the other hand, are a concept that is primarily associated with the medieval European feudal system rather than the Indian social structure. The term "knight" refers to a mounted and armored soldier serving a lord in medieval Europe and does not have any relevance or connection to the hierarchical classifications within Hindu society.

Understanding these classifications helps clarify the distinctions between different social systems globally and emphasizes that the caste system in Hinduism is unique to its cultural and historical context.