Quietism is a kind of philosophy where people believe that it's best to just be quiet, still and not do anything in response to the world or problems around them. You know how when you're really scared or worried, sometimes you just want to curl up into a little ball and not talk or do anything? That's kind of like quietism.
The people who follow this philosophy think that if they just stay quiet and inactive, then they won't cause any trouble or make anything worse. They believe that if they don't do anything, everything will work out alright eventually.
It's like if you're playing a game and you're not sure what move to make next, instead of making a move that might be wrong, you just wait and see what your opponent will do.
But some people think that quietism isn't a good philosophy because if everybody just stayed quiet and didn't do anything, then we wouldn't be able to make any progress or solve any problems. So, it's important to find a balance between being quiet and taking action when it's necessary.