ProtestantismTechnically, this term refers only to churches whose lineage dates back to the Reformation, when a series of principled protesters (protester, Protestant, get it?) broke away from the Roman Catholic Church.
In modern usage, this can include religions which are very similar to the religions that fit the definition above. Also religions that are very different from the definiton above, but just want to call themselves Protestant. Within Protestantism, there are many different subsets, including some with radically divergent beliefs.
See Martin Luther, Henry VIII, Jack Chick, Jesse Jackson, Ellen White, William Miller, Mormonism (sort of), Joseph Smith, Church of Christ Scientist (sort of), Mary Baker Eddy, Jerry Falwell, Pat Robertson, Jimmy Swaggart, Jim Bakker, Oral Roberts, Jerry Falwell ...