any unpleasant thick soft substance, such as food that has been cooked for too long

If you overcook the cabbage it'll turn to mush. 卷心菜烹得太久会烂糊的。

If you say your brain has turned to mush, it means you cannot think clearly.

If you describe something such as a book or film as mush, you mean that it is too emotional.

The movie was just romantic mush. 这部电影不过是部浪漫的煽情戏。