Imagine you are playing a game with your friends, and your friend always chooses the same thing. You notice that everyone else is choosing that thing too, because they think it's the best option.
Contrarian investing is kind of like that. It's when you choose the opposite thing that everyone else is choosing because you think it might be a better option.
For example, lots of people might want to buy a certain company's stock because they think it's a good investment. But a contrarian investor might choose to sell that same stock because they think it's overpriced or not as good of an investment as everyone else thinks.
It's like going against the crowd and doing the unexpected. Sometimes it works out really well, and sometimes it doesn't. But it's a way to try and make money by going against the norm.