What is untouchability?

It is the severe exclusion and discrimination of society practised against members of castes located at the bottom of the purity-pollution scale. They are not allowed even to touch the people falling in caste-hierarchy (Viz. Brahman, Ksatriya, Vaisya and Sudra). They are severly punished if eventually they are touched with members of all other castes and whosoever has been touched, would have go through elaborate purification rituals. In South India, notion of distant pollution or pollution due to shadow or merely vision/sight of an untouchable is still prevailing. Institution of untouchability thus, refers not just to the avoidance or prohibition of physical contact but to a much broader set of social sanctions.