Original: Before the first gospel was written (Mark, c 65-70), Paul the Apostle used the term gospel when he reminded the people of the church at Corinth "of the gospel I preached to you" (1 Corinthians 15.1).
Simplified: These books are the first part of the New Testament of the Bible, and are put in a group of this order: the Gospel of Matthew, the Gospel of Mark, the Gospel of Luke and the Gospel of John. The gospel is mostly about the Death and Resurrection of Jesus.