Untouchability is an extreme and vicious aspect of the caste system that prescribes stringent social sanctions against members of castes located at the bottom of the purity-pollution scale. These castes are considered so 'impure' that their mere touch severely pollutes members of all other castes, and they are placed outside the caste hierarchy.

The institution of untouchability refers not just to the avoidance of physical contact but to a much broader set of social sanctions. It has three main dimensions – exclusion, humiliation-subordination, and exploitation. Dalits face unique forms of exclusion, such as being prohibited from sharing drinking water sources or participating in collective religious worship, social ceremonies, and festivals. It is almost always associated with economic exploitation through forced, unpaid labour or confiscation of property. Untouchability is a pan-Indian phenomenon, though its specific forms and intensity vary across regions.