The word "Hindu" was of a far, far later origin; during the Greek period of history, Greeks and West Asians used the term Indu/Hindu with reference to the people living beyond the banks of the River Indus, and later the name began to be ascribed to the religion of the land also. 'Hindu' thus has only a geographical connotation and derivation; but, nevertheless, it has come to stay.
It is interesting to note that the word is not used by Indians in their descriptions or writings till the 17th century. If we go by the original definition of the word Hindu, any one who lives in the subcontinent is a Hindu and whatever religion he or she practices is Hinduism. The word Hindu is a secular word and literally translated it means Indian and the word Hinduism denotes any religion or religions that are practiced by the multitude of people living in the land beyond the river Indus.
The religion was used to be known as "Vaidika Dharma" or "Vedic Dharma" and even "Yoga Dharma"), as it has the Vedas for its authority and source (Vedokhilo Dharma Mulam) and its essence is Yoga. Thus is also more commonly known as Sanatana Dharma as it delineates and embodies values and doctrines which are of eternal validity.
Sanatana Dharma stands for "Rita" - the majesty of moral and spirtual law. It looks upon the whole universe as being under the purview of a moral law and subserving to the supremacy of God, its creator. Times may change, ages may roll by, continents may rise and disappear, but values of life like truth, love, compassion, one's duty to mother, father, preceptor and to fellow beings, and the eternal reality of the spirit and unity of all life, are truths and values that subsist and will subsist for ever. These are the eternal values and truths which are embedded in the Vedas and are embodied in the religion that had evolved out of Vedas. These values being of eternal validity and universality, are the justification for the religion that embody them, for being called as Sanatana Dharma, the eternal Dharma, law/religion.
Such a comprehensive teaching is evident in the many sided yogic and meditational practices of Hinduism, the vast culture of Hinduism including art, medicine and science, and in the Hindu recognition of the importance of all systems of knowledge, material, occult and spiritual. The social customs of Hinduism, with their emphasis on spiritual practices, are also based upon such universal truth, though some of them have departed from it through the long course of time. Hence they require adjustment in light of changing times.