In Christendom today, there are often considered to be three primary branches – Catholicism, Eastern Orthodox, and Protestantism (debating aside whether or not this is an accurate representation of current-day Christianity). Let’s first get started with the usual…

Dictionary.com

Protestantism

1. the religion of Protestants.
2. the Protestant churches collectively.
3. adherence to Protestant principles.

Protestant

noun

1. any Western Christian who is not an adherent of a Catholic, Anglican, or Eastern Church.
2. an adherent of any of those Christian bodies that separated from the Church of Rome during the Reformation, or of any group descended from them.
3. (originally) any of the German princes who protested against the decision of the Diet of Speyer in 1529, which had denounced the Reformation.

Etymonline.com

1640s, from French protestantisme or else formed from Protestant + -ism.

Discussion/Explanation

Protestantism and Protestant are terms inherently embroiled with everything involving the Reformation or Protestant Reformation. To see more on this particular and important historical time, see the page on the Protestant Reformation.

I would be a Protestant as I continue in the tradition and theology of Protestants everywhere who separate themselves from Catholicism (in particular). Protestants do not talk about the Eastern Orthodox much as it was from the western, the Roman Catholic, church that the Protestants separated from historically.

Protestantism today is spread throughout the globe. The United States of America was largely founded by those seeking a place to call their own (many of whom Protestants) who came here to escape various hardships as well as religious persecutions from where they came.

I would highly recommend checking out the link above to find out more as you will come to see much of what has made Protestantism different from the “Christianity” that came before.