Breaking down the question
This short note asks you to distinguish two major forms of Indian social organisation. The examiner wants precise defining features of each and a crisp contrast, not a long essay.
How to approach it
Define a tribe and then a caste, and contrast them on a few sharp axes — hierarchy, endogamy, occupation, ritual status and territorial identity. Close by noting the blurred boundary.
Model answer
A tribe is a territorially rooted community sharing a common name, dialect, ancestral belief and a relatively self-sufficient economy, marked historically by comparative isolation and egalitarian relations. A caste is a hereditary, endogamous group occupying a fixed rank within a graded hierarchy ordered by the idiom of ritual purity and pollution, and traditionally tied to a hereditary occupation.
The two differ on several counts. A tribe stands as a horizontal, largely egalitarian whole, whereas castes are vertically ranked. Tribal identity rests on territory and kinship; caste identity rests on ritual status and the wider varna order. Tribes were long outside the Hindu ritual scheme, while castes are integral to it. Occupation in a tribe is generalised; in a caste it is specialised and inherited.
Yet the distinction is not watertight. G. S. Ghurye read tribes as backward Hindus, while Surajit Sinha's notion of a tribe-caste continuum showed tribes gradually absorbed into the caste order through Sanskritisation, as with the Bhumij. The features of the caste system illuminate this process of integration.
Examiner's perspective
A four-mark note rewards clean definitions and a pointed contrast. Naming the tribe-caste continuum and one illustration signals command; padding with history weakens the answer within so tight a limit.