Originally it was used by Reformers to self identify themselves. Today it's usage is so mushy that it really has little practical meaning.
And the Catholic church does not consider itself a "people of the book":
Yesterday saw...a forceful plea from a key papal advisor [Bishop Salvatore Fisichella, the rector of the Lateran University and President of the Pontifical Academy for Life] to reject the idea of Christianity as a “Religion of the Book”...........the big debate over Dei Verbum at the time of the council pitted what was then known as the “two-source theory,” which held that Scripture and tradition are essentially two separate streams of revelation, against the “one-source theory,” which posited that Scripture is the lone source of revelation and tradition is an elaboration of it. In effect, Dei Verbum held that Scripture and tradition are interdependent and integrally related to one another.
-- from the thread Synod: Christianity not a 'Religion of the Book'
"As we begin the work of this synodal assembly, under the guidance of the Holy Spirit, let us turn our gaze to Christ, the light of the world and our only teacher," Cardinal Levada encouraged.The prelate's point was further developed when Cardinal Marc Ouellet, archbishop of Quebec, took the floor to affirm that the Word is much more than the Bible. He clarified that Christianity is not a religion of the Book.
"The Word of God means before all else God himself who speaks, who expresses in himself the divine Word that belongs to his intimate mystery," he said.
This Word, he added during his Latin-language discourse, which he delivered seated beside the Pope, speaks in a particular and also dramatic way in the history of man, especially in the election of a people, in the Mosaic law and the prophets.
-- from the thread Cardinal Says Scripture Inseparably United to Tradition
Evangelists were Matthew, Mark, Luke and John.
From Ancient Greek εὐαγγέλιον (euangelion)
evangelio (plural evangelioj, accusative singular evangelion, accusative plural evangeliojn)
ēvangeliō