"What a mess" is an expression of exclamation that something is really in a mess. It is commonly used to describe a situation that is disordered, untidy, or unpleasant. For example, if a room is very messy, someone might say "What a mess!" to express their frustration or disappointment. The phrase can also be used to describe a situation that is full of trouble or problems. In the Southern United States, the phrase "a mess" can sometimes mean "adorable and precocious," but this usage is not universal.