A comeback is a quick, witty reply. “Your mama” is a lame comeback but a popular one. It's also a return to prominence after a break, like an athlete who retires and then makes a comeback by returning to the sport.
If someone insults you, and you say something back that turns the insult around, that's a comeback. Nice job. Another comeback is when someone — especially in entertainment or sports — comes back after being gone. If a popular singer leaves music for a few years and then returns with a hit song, that's a comeback. In the song “Mama Said Knock You Out,” LL Cool J starts by saying, “Don’t call it a comeback, I been here for years!”