There are lots of answers to the question above, but I prefer the one found in Alister E. McGrath’s Christian Theology: An Introduction, second edition (1997). It isn’t perfect, but it’s better than many popular notions these days that link evangelicalism to a specific American political agenda. The description is as follows:
The term “evangelical” dates from the sixteenth century, and was then used to refer to Catholic writers wishing to revert to more biblical beliefs and practices than those associated with the late medieval church… The term is now used widely to refer to a transdenominational trend in theology and spirituality, which lays particular emphasis upon the place of Scripture in the Christian life. Evangelicalism now centers upon a cluster of four assumptions:
- The authority and sufficiency of Scripture.
- The uniqueness of redemption through the death of Christ upon the cross.
- The need for personal conversion.
- The necessity, propriety, and urgency of evangelism.
All other matters have tended to be regarded as adiaphora, “matters of indifference,” upon which a substantial degree of pluralism may be accepted….
Historically, evangelicalism has never been committed to any particular theory of the church, regarding the New Testament as being open to a number of interpretations in this respect, and treating denominational distinctives as of secondary importance to the gospel itself. This most emphatically does not mean that evangelicals lack commitment to the church as the body of Christ; rather, it means that evangelicals are not committed to any one theory of the church. A corporate conceptoin of the Christian life is not understood to be specifically linked with any one denominational understanding of the nature of the church. In one sense, this is a “minimalist” ecclesiology; in another, it represents the admission that the New Testament itself does not stipulate with precision any single form of church government, which can be made binding upon all Christians. This has had several major consequences, which are of central importance to an informed understanding of the movement.
- Evangelicalism is transdenominational. It is not confined to any one denomination, nor is it a denomination in its own right. There is no inconsistency involved in speaking of “Anglican evangelicals,” “Presbyterian evangelicals,” “Methodist evangelicals,” or even “Roman Catholic evangelicals.”
- Evangelicalism is not a denomination in itself, possessed of a disctinctive ecclesiology, but is a trend within the mainstream denominations.
- Evangelicalism itself represents an ecumenical movement. There is a natural affinity amongst evangelicals, irrespective of their denominational associations, which arises from a common commitment to a set of shared beliefs and outlooks. The characteristic evangelical refusal to allow any specific ecclesiology to be seen as normative, while honoring those which are clearly grounded in the New Testament and Christian tradition, means that the potentially divisive matters of church ordering and government are treated as of secondary importance.