What is the gospel supposed to mean? In what ways can it be used? What do Christians generally mean when they use the term "gospel"?
The word "gospel" is the Old English word for "good news" or "glad tidings" and has several different uses. It comes from the Greek word εὐαγγέλιον, euangelion (eu- "good", -angelion "message"). As an adjective, it is used in gospel choir or gospel music, perhaps to refer to the African American spiritual Christian hymn. As a noun, it is used in the phrase "to preach the gospel" or "to share the gospel", which means to evangelise. Evangelism is interpreted by many Christians to be a good thing, because they may say:
To outsiders of the faith, it just means to convert to Christianity.
Upon conversion to Christianity, it is expected that the person would be baptized. The means of baptism, however, varies from denomination to denomination. Refer to the conversation between Nicodemus and Jesus about baptism in John 3:1-10.
In short, there are two ways that gospel may refer to: (1) the act of converting to Christianity or (2) the life of the ideal Christian. Plus, the life of the ideal Christian may be a method to evangelism, an attempt to convert non-Christians into the Christian faith by making the Christian faith sound very attractive. Refer to "lifestyle evangelism".
The word gospel was actually in use prior to the birth of Jesus, and that context is crucial to understanding its meaning. The word gospel /euaggelion/ does literally mean "good news". It was employed by the Romans in the proclamation that Caesar was Lord. The fact that Caesar was "Lord" or emperor was asserted to be good news in that there would be no wars inside of the empire. However, those who were conquered by Caesar probably did not see such news as "good", but those in Rome likely did as they saw the expansion of their own influence. Indeed, to be a Roman citizen had significant privileges that went with it.
The assertion of the gospel of Jesus Christ, then, is that Jesus is Lord, not of a physical kingdom but of a spiritual kingdom. He is Lord of this Kingdom because of what He accomplished through His death and resurrection. Jesus has, indeed, conquered, but He didn't conquer mankind. He conquered mankind's greatest enemies--sin and death.
Thus, the gospel of Jesus Christ is the good news that Jesus has conquered our greatest enemies--sin and death--and that we can be freed from slavery in the kingdom of darkness and enter into the Kingdom of God as sons and daughters of the King Himself.