What is the gospel?

The Gospel: An Outline

Jesus the king

1. preexisted with the Father,
2. took on human flesh, fulfilling God’s promises to David,
3. died for sins in accordance with the Scriptures,
4. was buried,
5. was raised on the third day in accordance with the Scriptures,
6. appeared to many,
7. is seated at the right hand of God as Lord, and
8. will come again as judge.—Matthew Bates in Salvation by Allegiance Alone, 74

<idle musing>
Straight out of 1 Cor 15. It's usually called the kerygma, a Greek word meaning announcement. Unfortunately, most people truncate the gospel to items 3 through 5, possibly including 6 as an afterthought. They totally neglect the other ones, which are what frame the gospel and make it Good News.
</idle musing>