definition of true Christians, or is it fundamentalists?
Fundamentalist Christianity is a fundamentalist movement, especially within American Protestantism.
The term, Fundamentalist, tends to have a variable meaning. Historically, and for those who use the name to describe themselves, a Fundamentalist Christian is one who holds to all of the five Fundamentals of the Faith as a bare-minimum definition of Christian faith (see the Brief History of Christian fundamentalism below).
Derivatively, a fundamentalist Christian is a Christian who holds the Bible to be infallible, historically accurate, and decisive in all issues of controversy that the Bible is believed to directly address; which was the central issue for which the Christian Fundamentalist movement has contended.
AND FROM THE OXFORD DICTIONARY OF THE CHRISTIAN CHURCH:
What is a fundamentalist Christian?
From the Christian perspective, fundamentalist has traditionally referred to any follower of Christ who believes that the Bible is the inspired Word of God and who believes in its literal interpretation and fundamental teachings. The fundamental Christian believes in the experience of the "new birth" which occurs when faith is placed in Christ as Savior and Lord. To the world this may be viewed as radical, but is very basic to the Christian faith.
The idea of Christian Fundamentalism first emerged as a movement in the 19th century within various Protestant bodies, who reacted against the rising tide of evolutionary theories and modernist Biblical criticism. From a Bible conference of Conservative Protestants meeting in Niagara in 1895, a statement was issued containing what came to be known as the five points of fundamentalism: The verbal inerrancy of Scripture, the divinity of Jesus Christ, the virgin birth, a substitutionary theory of the atonement, and the physical resurrection and bodily return of Christ.¹ In the first half of the 20th century, most Protestant churches in the U.S. were divided into either Fundamentalist or Modernist groups. The term has generally been applied to all those who adhere to strict, conservative (Protestant) orthodoxy in the matter of Biblical inspiration.
In the broad sense, fundamentalism may be used to describe Christians who are uncompromising, conservative and who take their beliefs to the maximum — exactly how every believer should live.