美眉/MM [měi  méi]  n.

Originally this term referred to a pretty young girl, later it was used to call any young girl.  MM is the acronym based on the pinyin pronunciation.

Today at the school library I came across a MM, her appearance average. After reading and studying for a long time, she put her head down to doze on the desk. Then she forced herself to sit up and took out a mirror she carried with her. I saw her stare at the mirror for a long time and then say: “Look at you! Not pretty and still you don’t study hard!! What are you going to do in the future!!” After saying this, she resumed studying energetically.