Hinduism is a religious tradition that originated in the Indian subcontinent.
Hinduism is often referred to as Sanatana Dharma by  its practitioners, a
Sanskrit phrase meaning "the eternal law" or "eternal way".

Hinduism is one of the oldest religious traditions that  are  still  practiced,
and is the oldest major world religion. Among its roots  is  the  historical
Vedic religion of Iron Age India. Full of  diverse  beliefs  and  traditions,
Hinduism has no single founder. Its  sub - traditions  and  denominations
taken together add up to Hinduism qualifying as the world's third largest
religion following Christianity  and  Islam,  with  approximately  a  billion
adherents, of whom about 905 million  live  in  India  and  Nepal. Other
countries with large Hindu populations  include  Bangladesh, Sri  Lanka,
Pakistan,  Indonesia,  Malaysia,  Singapore,  Mauritius,  Fiji,  Suriname,
Guyana, Trinidad and Tobago, United Kingdom and Canada.

A Hindu is an adherent of the philosophies and  scriptures  of  Hinduism, a  set  of  religious,  philosophical  and cultural systems that originated  in the Indian subcontinent. The  actual  term  “Hindu”  first  occurs as  a  Persian geographical term (derived from the river sindhu), to identify  the  people  who  lived  beyond  the  River  Indus. However the modern origin is derived from the Arabic texts Al-Hind  referring  to  the  people  of  modern  day India and then got adopted as Hindu. In the world history “Hindu” was also used  by  all  Mughal  Empires  and towards the end  of  the  eighteenth  century  by  the  British  to  refer to the  people of “Hindustan”, the area of northern and adjoining northwestern India. Eventually “Hindu” became equivalent  and appropriate  to  anybody of “Indian” origin who was not otherwise Sikh, Jain,  or  belonged  to  a  religion  of  Abrahamic  denomination, thereby encompassing a wide range of religious beliefs and practices.

One of  the  accepted  views is that “ism” was added to “Hindu” around 1830 to denote the culture and religion of   the  high-caste  Brahmans  in  contrast  to  other  religions. The  term  was  soon  appropriated   by  Indians themselves as they tried to establish a national identity opposed to colonialism.

Thus  some  scholars  argue  tha t the  Hinduism is not a religion per se but rather a reification of a diverse set of traditions and  practices  by  scholars  who  constituted  a unified system and arbitrarily labeled it Hinduism. The usage may also have been necessitated by the desire  to  distinguish  between "Hindus"  and  followers  of  other religions during the periodic census undertaken by the colonial British government in India. Other scholars, while seeing Hinduism as a 19th century  construct, view  Hinduism  as  a  response  to British  colonialism  by I ndian nationalists who  forged  a  unified  tradition  centered  on  oral and written Sanskrit texts adopted as scriptures.
A commonly held view, though, is that while Hinduism contains both "uniting and dispersing tendencies", it has a common central thread of philosophical concepts (including  dharma,  moksha  and  samsara),  practices  (puja, bhakti etc) and  cultural  traditions. These  common  elements  originating  (or  being  codified within) the Vedic, Upanishad and Puranic scriptures and epics. Thus a Hindu could :
*  follow any of the Hindu schools of philosophy, such as Advaita  (non-dualism), Vishishtadvaita  (non-dualism     of the qualified whole), Dvaita (dualism), Dvaitadvaita (dualism with non-dualism), etc.
*  follow a tradition centered on any particular form of  the Divine, such  as  Shaivism,  Vaishnavism,  Shaktism,
    etc.
*  practice any one of  the various  forms  of  yoga  systems;  including  bhakti  (devotion)  in  order  to  achieve     moksha.

In 1995, while considering the question "who are Hindus and what are the broad features of Hindu religion", the Supreme  Court  of   India  highlighted  Bal   Gangadhar  Tilak's  formulation  of   Hinduism's  defining  features: Acceptance of  the  Vedas  with  reverence;  recognition of  the  fact  that  the  means  or  ways to salvation are diverse; and the realization of the truth that the number of  gods to be  worshipped  is  large, that  indeed  is  the distinguishing feature of Hindu religion.

Some thinkers have attempted to distinguish between the concept of Hinduism as a religion, and  a  Hindu  as  a member of a nationalist or socio-political class. Veer Savarkar  in  his  influential  pamphlet  Hindutva: Who is  a Hindu? considered geographical unity, common culture and common race to be the defining qualities of  Hindus; thus a Hindu was a person who saw India "as his Fatherland as well as his Holy land, that is, the cradle  land  of his religion". This conceptualization of Hinduism, has led to establishment of Hindutva as the  dominant  force  in Hindu nationalism over the last century.