The word “Hindu” is not a Sanskrit word. It was given by the Muhammadans. There is a river, Indus, which in Sanskrit is called Sindhu. The Muhammadans pronounce s as h. Instead of Sindhu, they made it Hindu. So “Hindu” is a term that is not found in the Sanskrit dictionary, but it has come into use. But the real cultural institution is called vanasrama. There are four varnas (social divisions) – brahmana, ksatriya, vaisya, and sudra – and four ashrams (spiritual divisions) – brahmacari, grhastha, vanaprastha, and sannyasa. According to the Vedic concept of life, unless people take to this system or institution of four varnas and four ashrams, actually they do not become civilized human beings. One has to take this process of four divisions of social orders and four divisions of spiritual orders; that is called varnasrama. India’s culture is based on this age-old Vedic system.
Source: A.C. Bhaktivedanta Swami Prabhupada (2014 edition), “The Science of Self-Realization”, Page 201, 227