In the Bible "the gospel" (from the Greek "euangelion," meaning "good news") refers to the message about Jesus Christ; Mark opens his book with the phrase.
Mark 1:1 in the King James Version reads:
The beginning of the gospel of Jesus Christ, the Son of God;
The verse is the opening line of the Gospel of Mark, the shortest of the four Gospels. Read it in context at Mark 1:1, or the full chapter at Mark 1. Encyclopedia entry: en.wikipedia.org/wiki/The_gospel.