Protestants reject the Roman Catholic Church's doctrine that it is the one true church, believing in the invisible church, which consists of all who profess faith in Jesus Christ. Some Protestant denominations are less accepting of other denominations, and the basic orthodoxy of some is questioned by most of the others. Individual denominations also have formed over very subtle theological differences. Other denominations are simply regional or ethnic expressions of the same beliefs. Because the five solas are the main tenets of the Protestant faith, non-denominational groups and organizations are also considered Protestant.
If it is possible to answer this question, answer it for me (else, reply "unanswerable"): What other entities are also considered to be Protestant?
non-denominational groups and organizations