Evangelicalism is the idea, concept, association, or in the case of an evangelical, system of action for spreading one's faith, specifically the Christian faith, to sinners in correspondance with the Great Commission. The Bible only mentions a word like "evangelism" once, where Paul says something about "evangel" I think, (Might want to cite this, I know there's something in there about something.) but the Bible does give a good bit of guidelines for sharing our faith, even if it does not specifically lump everything together under an "Evangelical chapter".