I am neither a poem nor anyone's mountain lake. What do you mean?

Not owned or defined by anyone. This sentence can be understood as expressing a unique identity or way of existence. "I am not a poem" means that I am not a work of art, and I am not described or defined by poetry. "It is nobody's mountain lake" means that it is not owned or defined by anyone, and it is not a landscape or attribute owned by others. The meaning of the whole sentence can be understood as an independent individual who is not limited by the definition of others. It has its own characteristics and way of existence and does not belong to anyone's abstract description or classification. This sentence is also an expression of freedom and individuality, emphasizing the importance of unique identity and independent thinking.