Short answers, pulled from the story.
There are approximately 1.17 billion Hindus worldwide, accounting for 14.9% of the global population. Pew Research projects the number will rise to 1.4 billion by 2050. Hindus are the world's third-largest religious group after Christians and Muslims.
The word Hindu derives from the Sanskrit word Sindhu, meaning a large body of water, which was the name of the Indus River. The earliest known use of a form of the word appears in the 5th-century BCE DNa inscription of the Persian king Darius I, referring to the province of Hindush in northwestern India. It began as a geographical term for people living near or beyond the Indus River, not a religious label.
India and Nepal are the only two Hindu-majority countries, together accounting for more than 95% of the global Hindu population. After them, the countries with the largest Hindu populations are Bangladesh, Pakistan, Indonesia, Sri Lanka, the United States, Malaysia, the United Arab Emirates, and the United Kingdom. These ten countries together account for 99% of all Hindus worldwide.
The earliest known use of Hindu in a religious context in a European language was in 1649, in a Spanish-language publication by the Christian friar Sebastiao Manrique. In Indian texts, the poet Vidyapati's Kirtilata from 1380 uses the term in the sense of a religion. DN Jha's historical research argues that no Indians described themselves as Hindus before the 14th century.
No single set of beliefs is required. Hindus can choose to be polytheistic, pantheistic, monotheistic, monistic, agnostic, atheistic, or humanist, and there is no ecclesiastical order, no unquestionable religious authority, and no single founding prophet. Chief Justice P. B. Gajendragadkar stated in a 1995 Indian Supreme Court ruling that Hinduism does not claim any one prophet, worship any one god, or subscribe to any one dogma.
British colonial scholars and legal systems broadened and reshaped the term. The Asiatick Researches, founded in the 18th century, initially treated all Indian religions including Buddhism as subgroups of Hinduism, before gradually separating out Sikhism, Buddhism, and Jainism as distinct categories. Colonial Anglo-Hindu law at one stage applied the term Hindu to followers of Judaism and Zoroastrianism as well as Indian religions. Historian DN Jha summarised the result: the British borrowed the word, gave it a new meaning, and reimported it into India as a reified phenomenon called Hinduism.