Another term that is somewhat gray in its paramaters to me (despite all my life being a Presbyterian Christian) is the term, as in political demographics, evangelical Christians.


 Quote:

evangelical

1. Also, evangelic. pertaining to or in keeping with the gospel and its teachings.


2. belonging to or designating the Christian churches that emphasize the teachings and authority of the Scriptures, especially of the New Testament, in opposition to the institutional authority of the church itself, and that stress as paramount the tenet that salvation is achieved by personal conversion to faith in the atonement of Christ.


3. designating Christians, especially of the late 1970s, eschewing the designation of fundamentalist but holding to a conservative interpretation of the Bible.


4. pertaining to certain movements in the Protestant churches in the 18th and 19th centuries that stressed the importance of personal experience of guilt for sin, and of reconciliation to God through Christ.


5. marked by ardent or zealous enthusiasm for a cause.


noun


6. an adherent of evangelical doctrines or a person who belongs to an evangelical church or party.



The portion that rings most true for me:

 Quote:
evangelical in Culture:

A member of any of various Christian churches that believes in the sole authority of the literal Bible, a salvation only through regeneration, or rebirth, and a spiritually transformed personal life.


Although that still leaves quite a bit of wiggle room and ambiguity, where you could include or exclude any denomination of Christians you want in how you define "evangelicals".