Dharma refers to the sustaining principle of the universe. Sanatana Dharma, that is adopted by the Indian society, refers to an unbroken tradition of Dharma from time immemorial. Sanatana Dharma manifests as a society adhering to Varna Dharma. The society adhering to the Varna Dharma includes four Varnas – Brahmana, Kshatriya, Vysya, and Shudra. There is no fifth Varna.
Varna dharma continues mainly through family traditions and jaati associations. Inter Varna/jaati marriages generates newer jaatis. The continuation of jaati traditions through endogamous marriages could be in alignment with the Sanatana Dharma.
The four fold of Varna society is a highly evolved system aimed at ensuring ideal environment and path for all round development of all individuals in the society.
Those who are incapable of adhering to the established Varna System are expelled from the respective adherents of Varnas and are referred as ‘Dasyus’. It should noted that Dasyus have a jaati and possibly a Varna identity and are either aligned or well positioned to be aligned to the ancient tradition. Those who are not familiar with the Varna Dharma or not in a position to follow the ancient tradition are referred to as Mlecchas. Those who are not able to understand or harbor antagonistic attitude and stay unfamiliar with the Varna Vyavastha are included in this ‘Mlecchas’.
Hindu is a term primarily used to refer to the followers of ancient tradition based on Vedas by the outsiders. Presently, the term is used loosely with slightly different meanings. In general, these meanings have positive connotations, especially with an intent of social harmony. Some others use the term to include Buddhists, Sikhs and Jains. Some would like to use the term to refer to all Indian nationals. Those who would like to establish a harmonious society by establishing a uniform society would prefer the community who identify themselves as the custodians of the ancient tradition as Hindus. Some use the term to refer to those who have non-antagonistic attitude towards the ancient tradition.
Thus the adherents of ancient tradition is described either in terms of Varna, or in terms of jaati or by the term Hindu. It is interesting to note that those who identify themselves primarily through Varna and Jaati identity also would consider themselves as Hindus. On the other hand, some of those who would like to identify themselves primarily by Hindu identity, would not like to be identified by their Varna / Jaati identity.
Thus, it is safe to conclude that the Hindu identity is a buffer identity shielding the Sanatana Dharma from the onslaught of barbarism. Thus, the Dharmic tradition is sustained by four Varnas supported by Jaati traditions. Dasyus uphold the jaati traditions. Hindus facilitate Dasyus to get integrated with the jaati traditions and simultaneously try to uplift Mlechhas towards the ancient tradition.
To clarify, Chandala is a Shudra, a fallen Brahamana may be a Dasyu. Jihadi Muslims, Proselytizing Christians, extremist Naxals, and unfriendly Jews are all Mlechhas. Hindus are those who are claimants of ancient tradition with or without jaati/varna association. Those who have non-antagonist attitude towards the ancient tradition may also be referred to as Hindus.