Very basically, Protestantism (coming from the Latin word protestari to protest) refers to religions formed after the Reformation during sixteenth century Europe. These groups rejected the teachings of the Roman Catholic Church, beginning with Henry VIII, and his daughter Elizabeth, I in the sixteenth century. The Roman Catholic Church had also fallen into gross corruption. Protestants believe that the Bible is their only source of authority and inspiration, unlike the Roman Catholic Church, The Eastern Rite Religions and other Orthodox religions who believe that their tradition of belief is equal to the Bible. They also reject the notion of "Apostolic Succession" which is the belief of the Roman Catholic Church eg. the pope is the direct descendent of Saint Peter who is believed by them, to have been by appointed by Jesus. The sacramental nature of the clergy is also rejected by Protestants. This means that any person who enters the ranks of the clergy does so by the laying on of hands by the higher clergy who are believed to be descended from Jesus' apostles.
Other religious groups to form following the Reformation are Lutheranism, Methodism, the Baptist church, Presbyterianism and Calvinism.