This is as good of a definition as any I’ve seen.
[ee”-van-jel”-ih-kul] (Greek euangelion, “good news” or “gospel”)
A transdenominational term that finds roots in the historic church, but most commonly, from a theological standpoint, represents those who identify with historic Protestantism and are committed to 1) the necessity of conversion to Christ, 2) the authority of Scripture, 3) the spread of the Gospel message, 4) a belief in the Five Solas of the Reformation, 5) a belief in the Nicene Creed and Chalcedonian statement of faith. Evangelicalism is not represented by any leader or institutional structure, but is representative of an ethos the permeates many Christian traditions.
HT: Paul Dare