The term pagan is used, today, to signify people who do not believe in the monotheistic god of Christianity, Judaism, and Islam. It is used much like “heathen.” It also refers to pantheists and neo-pagans.
Origins of the Word Pagan
Pagan comes from a Latin word paganus, meaning villager, rustic, civilian, and itself comes from a pāgus which refers to a small unit of land in a rural district. It was a demeaning Latin term (like the word hick), that originally lacked a religious significance.
Etymology Online says pagan comes from a PIE base *pag- ‘to fix’ and related to the word “pact”. It adds that the usage to refer to nature worshipers and pantheists dates from 1908.