In an article by Robert M. Bowman Jr. on Mormonism, he begins the article with an insightful overview of Christianity through the lens of a 5-ring delineation of churches that are included in the religion of Christianity. What is noteworthy is who is included in the 5th ring, which is generally regarded as technically not Christian in terms of the validity/soundness of their expression of Christian faith:

Christianity includes an incredible diversity of belief and practice. (The numbers I use here are extremely rough approximations for sake of getting the big picture.) (1) About a billion people—about half of all Christianity—are found in the Catholic Church. (2) About a quarter of a billion people belong to one of the Orthodox or Eastern churches (which includes Greek Orthodox, Russian Orthodox, etc., and also the Coptics and other groups). (3) Nearly a third of a billion people are associated with some conservative Protestant church or movement, either evangelical Protestant or Pentecostal. (4) Another quarter of a billion people belong to mainline, mostly moderate to liberal, Protestant denominations.

(5) This leaves roughly a quarter of a billion people whose forms of Christianity do not fit into any of the aforementioned categories. Within this none-of-the-above category is a wildly diverse assortment of religious communities. If each major type of Christianity represented in this fifth category were its own species, it would look like the Mos Eisley Cantina on Tatooine or an assemblage of delegates to a parliamentary meeting of the United Federation of Planets (take your pick!). It includes (deep breath) Adventism, British-Israelite groups, Christian Science, the Family, Jehovah’s Witnesses, Latter-day Saints, Messianic Judaism, Metropolitan Community Churches, New Thought, Oneness Pentecostalism, Rosicrucianism, the Sacred Name movement, Swedenborgianism, the Unification Church, Unitarian Universalism, The Way International, and many, many others.

Read Bowman’s entire article here.