A caste is a fixed social group into which an individual is born within a particular system of social stratification: a caste system. Within such a system, individuals are expected to: marry exclusively within the same caste (endogamy), follow lifestyles often linked to a particular occupation, hold a ritual status observed within a hierarchy, and interact with others based on cultural notions of exclusion, with certain castes considered as either more pure or more polluted than others. Its paradigmatic ethnographic example is the division of India's Hindu society into rigid social groups. Its roots lie in South Asia's ancient history and it still exists. However, the economic significance of the caste system in India has been declining as a result of urbanisation and affirmative action programs. A subject of much scholarship by sociologists and anthropologists, the Hindu caste system is sometimes used as an analogical basis for the study of caste-like social divisions existing outside Hinduism and India. The term "caste" is also applied to morphological groupings in eusocial insects such as ants, bees, and termites.
The English word caste (kɑːst,_kæst) derives from the Spanish and Portuguese casta, which, according to the John Minsheu's Spanish dictionary (1569), means "race, lineage, tribe or breed". When the Spanish colonised the New World, they used the word to mean a 'clan or lineage'. It was, however, the Portuguese who first employed casta in the primary modern sense of the English word 'caste' when they applied it to the thousands of endogamous, hereditary Indian social groups they encountered upon their arrival in India in 1498. The use of the spelling caste, with this latter meaning, is first attested in English in 1613. In the Latin American context, the term caste is sometimes used to describe the casta system of racial classification, based on whether a person was of pure European, Indigenous or African descent, or some mix thereof, with the different groups being placed in a racial hierarchy; however, despite the etymological connection between the Latin American casta system and South Asian caste systems (the former giving its name to the latter), it is controversial to what extent the two phenomena are really comparable.