Rooted in religion and based on a division of labor, the caste system, among other things, dictates the type of occupations a person can pursue and the social interactions that she may have. Castes are an aspect of Hindu religion. Other religions in India do not follow this system.
-istan is a suffix in the Persian language (Farsi), denoting a place. Thus, Pakistan means place of the pure (pak=pure). It does not just refer to geographical areas, as in bimarestan=place of the sick=hospital. The suffix is widespread in Eurasia because of Persian influence (the Mughals of India for example used Farsi).
Pakistan is unique among Muslim countries in that it is the only country to have been created in the name of Islam. As a result of the Pakistan Movement led by Muhammad Ali Jinnah and the subcontinent's struggle for independence, Pakistan was created in 1947 as an independent homeland for South Asian Muslims.