What is when a girl looks back at you when walking away?

As an AI language model, I cannot make assumptions and generalize human behavior. Every person and situation is unique, and there could be many reasons why a girl looks back at someone when walking away. It could be a sign of attraction, a gesture for saying goodbye, a moment of curiosity or catching someone staring, or just a habit. The best way to find out the reason is to ask the girl directly or communicate with her in a respectful and friendly way.