I know the word itself means "of or related to the gospel." That's not what I'm talking about. I mean, when the term is used to refer to a subset of Christians, what are the characteristics being implied? What is the criteria used to determine what Christians are "Evangelicals" and which ones aren't?
Evangelicalism is a branch of protestantism, so it involves a protestant understanding of the gospel. But not all protestants are evangelical.
I think the biggest distinctive is what they say about the Bible. They reject those who say the Bible is flawed in some way, not relevant for today, that you need the authority of church leaders to understand it, or that God gives new relevations today that take priority over the Bible. To quote from the Gospel Coalition:
Revelation God has graciously disclosed his existence and power in the created order, and has supremely revealed himself to fallen human beings in the person of his Son, the incarnate Word. Moreover, this God is a speaking God who by his Spirit has graciously disclosed himself in human words: we believe that God has inspired the words preserved in the Scriptures, the sixty-six books of the Old and New Testaments, which are both record and means of his saving work in the world. These writings alone constitute the verbally inspired Word of God, which is utterly authoritative and without error in the original writings, complete in its revelation of his will for salvation, sufficient for all that God requires us to believe and do, and final in its authority over every domain of knowledge to which it speaks. We confess that both our finitude and our sinfulness preclude the possibility of knowing God’s truth exhaustively, but we affirm that, enlightened by the Spirit of God, we can know God’s revealed truth truly. The Bible is to be believed, as God’s instruction, in all that it teaches; obeyed, as God’s command, in all that it requires; and trusted, as God’s pledge, in all that it promises. As God’s people hear, believe, and do the Word, they are equipped as disciples of Christ and witnesses to the gospel.
Why is the movement called evangelicalism when it's primary distinctive isn't about the gospel? I think because historically the people they were reacting against neglected the gospel because they neglected the Bible. Promoting the authority of the Bible is a safeguard to ensure the gospel keeps first importance.
The Barna Group is a Christian polling firm that does public opinion studies. In their research, they classify people into different belief groups. Rather than allow people to self identify themselves as born again or evangelical, they ask people if they agree with certain statements, and classify people based on their answers. The criteria for the classifications are at the end of each report that they produce. (For example, here is a recent report from December 2013 titled "Is Evangelism Going Out of Style?")
For the purposes of their studies, "Born again Christians" are people who have met this criteria:
- They say they have made "a personal commitment to Jesus Christ that is still important in their life today."
- They believe that when they die they will go to Heaven because they had confessed their sins and had accepted Jesus Christ as their savior.
In their studies, "Evangelical" Christians are those who meet the "born again" criteria above, plus seven other conditions:
- saying their faith is very important in their life today;
- believing they have a personal responsibility to share their religious beliefs about Christ with non-Christians;
- believing that Satan exists;
- believing that eternal salvation is possible only through grace, not works;
- believing that Jesus Christ lived a sinless life on earth;
- asserting that the Bible is accurate in all the principles it teaches; and
- describing God as the all-knowing, all-powerful, perfect deity who created the universe and still rules it today.
When classifying people in these groups, they do not ask people to describe themselves as "born again" or "evangelical," as people can have different ideas about what these terms mean. The groups are also not dependent on church affiliation.