CHRISTIAN HISTORY TODAY – What is a Protestant? Today we know it as the movement that broke away from the Roman Catholic Church that began in earnest with Martin Luther in 1517. It wasn’t until the 2nd Diet of Speyer that started on April 20, 1529. A “diet” is a Latin term that essentially means a meeting of church folks to work through some issue. Luther was excommunicated at the Diet of Worms in 1521 and by 1529 more diets occurred around this Lutheran movement. When this second diet occurred at Speyer in Germany (a modern picture shown here) the reformers issued a Protestatio and from this Latin word we get the term Protestant.