Okay kiddo, do you know what a gun is? It's a tool that people use to shoot things. A Puckle gun is a special kind of gun that was invented a long time ago, way back in 1718.
It was a big, clunky gun that could shoot round bullets. But the really cool thing about the Puckle gun was that it had a special magazine that could hold lots of bullets all at once. That way, the person using the gun didn't have to stop and reload after every shot like they would with a regular gun.
The Puckle gun was designed to be used by ships to defend themselves against other ships. But it wasn't very popular because it was hard to use and not very easy to handle. Eventually, people stopped using it and it became just a thing of the past.
So, that's what a Puckle gun is, a big gun with a special magazine to shoot lots of bullets that was invented a long time ago.