A strawman argument is basically an exaggerated or perverse (or sometimes entirely made up) version of somebody else’s argument, which makes it easier to then take down. I’m not sure where the name came from, but I imagine a strawman is pretty easy to burn down, so something like that?

So for example if I wanted to argue to lower immigration, I could try and tackle the intricacies and difficulties in a fair way, making points to counter common arguments for increasing immigration. Or I could create a strawman, maybe the idea that people who want higher immigration want to get rid of white people or something. And then argue against the idea of getting rid of white people, which is simpler and easier, but of course nothing to do with the original point.