What is what does it mean when a girl smiles at you when you walk by?

As an AI language model, I do not have personal experiences and feelings, but I can provide some general information that might be helpful. When a girl smiles at you when you walk by, it could mean different things depending on the situation. It could be a sign of friendliness, politeness, or a genuine interest in getting to know you. However, it doesn't necessarily mean that she likes you romantically or wants to start a relationship with you. It's important to consider the context of the situation and the girl's body language and behavior to get a better understanding of her intentions. If you're interested in her, you can try initiating a conversation or asking her out to get to know her better.