The Good News is a message about Jesus Christ. It's in the Bible, Romans 1:2-3, TLB. "This Good News was promised long ago by God's prophets in the Old Testament. It is the Good News about His Son, Jesus Christ our Lord, who came as a human baby, born into King David's royal family line."
What is the Good News? It's in the Bible, Mark 1:14-15, NIV. "After John was put in prison, Jesus went into Galilee, proclaiming the good news of God. 'The time has come, he said. 'The kingdom of God is near. Repent and believe the good news!'"