Mormonism is the predominant religious tradition of the Latter Day Saint movement of Restorationist Christianity started by Joseph Smith in Western New York in the 1820s and 30s.
After Smith was killed in 1844, most Mormons followed Brigham Young on his westward journey to the area that became the Utah Territory, calling themselves The Church of Jesus Christ of Latter-day Saints (LDS Church).
Other sects include Mormon fundamentalism, which seeks to maintain practices and doctrines such as polygamy, and various other small independent denominations.
The second-largest Latter Day Saint denomination, the Reorganized Church of Jesus Christ of Latter-day Saints, since 2001 called the Community of Christ, does not describe itself as “Mormon”, but instead follows a Trinitarian Christian restorationist theology, and also considers itself Restorationist in terms of Latter Day Saint doctrine.
The word Mormon originally derived from the Book of Mormon, a religious text published by Smith, which he said he translated from golden plates with divine assistance.
The book describes itself as a chronicle of early indigenous peoples of the Americas and their dealings with God. Based on the name of that book, early followers of Smith were more widely known as Mormons, and their faith was called Mormonism. The term was initially considered pejorative, but Mormons no longer consider it so (although generally preferring other terms such as Latter-day Saint, or LDS).
Mormonism shares a common set of beliefs with the rest of the Latter Day Saint movement, including use of and belief in the Bible, as well as in other religious texts including the Book of Mormon and Doctrine and Covenants. It also accepts the Pearl of Great Price as part of its scriptural canon, and has a history of teaching eternal marriage, eternal progression, and polygamy (plural marriage) (although the LDS Church formally abandoned the practice of plural marriage in 1890).
Cultural Mormonism, a lifestyle promoted by Mormon institutions, includes cultural Mormons who identify with the culture, but not necessarily with the theology. – Wikipedia https://tinyurl.com/or6qt8p