The word gospel means good news. The good news is that Jesus Christ has made a perfect atonement for mankind that will redeem all mankind from the grave and reward each individual according to his/her works.
So, the gospel is God’s plan of salvation, made possible through the atonement of Jesus Christ. The gospel includes all of the eternal truths or laws, covenants, and ordinances needed for mankind to enter back into the presence of God. God restored the fullness of the gospel to the earth in the 1800s through the Prophet Joseph Smith.
Which is why it so important to tell the whole world about these things!