The (canonical) Gospels are the first four books of the New Testament (Matthew, Mark, Luke and John) containing the events of Jesus Christ’s life and his teaching. Essentially, they offer the message of salvation from personal sin through God’s forgiveness.
Non-believers often point out apparent contradictions among the different accounts while believers usually see them as presenting a holistic harmony, not unlike four-channel audio that amplifies a single message.
Wikipedia nicely outlines the etymology of the word Gospel:
The word gospel derives from the Old English gōd-spell  (rarely godspel), meaning “good news” or “glad tidings”. It is a calque (word-for-word translation) of the Greek word εὐαγγέλιον, euangelion (eu- “good”, -angelion “message”). The Greek word euangelion is also the source (via Latinised evangelium) of the terms “evangelist” and “evangelism” in English. The authors of the four canonical Christian gospels are known as the four evangelists.¹
There are other so-called gospels that are not recognized by most Christian Churches as canonical.² They may, however, be acknowledged as offering some insights or points of interest concerning the total situation in the ancient world around the time of Jesus. On the down side, Church officials usually teach that non-canonical gospels might complicate things or distract otherwise genuine seekers, making it harder for them to find the true light of God.
Again, this is what most Christian Church officials will say. Contemporary Gnostics and New Age enthusiasts, however, would probably fire back that dried up and hypocritical Church structures and teachings would get in the way of their finding God, just as much if not more than a few allegedly misguided passages in a non-canonical gospel.
² For a list of these see http://en.wikipedia.org/wiki/Gospel#Non-canonical_gospels
- Gospel of Luke (earthpages.wordpress.com)
- Gospel of Mark (earthpages.wordpress.com)
- Gospel of John (earthpages.wordpress.com)
- Gospel of Matthew (earthpages.wordpress.com)
- Gospel Life (garrettventry.wordpress.com)
- The earliest gospels – Marcion’s gospel (according to P.L. Couchoud) (vridar.wordpress.com)