Here's the definition of the Gospel listed in the New Believer's Bible New Testament in the "GLOSSARY OF CHRISTIAN TERMS":
"Gospel: 1. The "Good News" of salvation; the explanation of how one can be saved from the eternal punishment of hell and receive forgiveness and eternal life through Jesus Christ (see 1 Corinthians 15:1-5, page 205). 2. This term in the plural refers to the first four books of the New Testament."1
1 New Believer's Bible New Testament (Carol Stream, IL: Tyndale House Publishers, Inc., 2006), p. 374.