An evangelical Christian is basically one for whom the Bible is the final authority for faith and life. This contrasts with Christians for whom the Bishop of Rome is the final authority, or Tradition. Some who claim to be Christians make religious feeling the final authority, such as those known as theological liberals, but surely that stretches the term Christian too far (see Christianity and Liberalism by Gresham Machen).
Evangelical Christians, or Evangelicals for short, receive the Bible as the Word of God, the final authority for faith and life. A corollary to this is that Evangelicals can only approach the text of the Bible with reverence and wonder, and not critically, that is with skepticism or doubt. Critical biblical scholarship is thus not for Evangelicals. Another corollary is that for Evangelicals all subjects must align with the text of the Bible. Hence Evangelicals approach the world with awe and wonder, as realists rather than anti-realists.
Evangelicals are not united on all matters. There are some significant divergences, notably: (1) baptism of infants and adults or only adults, (2) Eucharist/communion as the Body and Blood of Christ or only symbols, (3) some church hierarchy or only congregations, (4) continuationism or cessationism with regard to miracles and the gifts of the Spirit, and (5) emphasis on believers receiving Christ or deciding for Christ.