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

When a girl smiles at you as you walk by, it can mean a variety of things depending on the context and her demeanor. Here are a few possible interpretations:

1. Friendly Gesture: The smile could simply be a polite or friendly gesture. Smiling is a common social signal to acknowledge someone else's presence in a warm and positive way.

2. Interest or Attraction: In some cases, a smile might indicate that she finds you attractive or is interested in getting to know you better. It might be accompanied by other body language cues, such as prolonged eye contact or a slight blush.

3. Recognition: If she knows you or recognizes you from somewhere, the smile might be a way of acknowledging your presence because she remembers or knows you.

4. Politeness: Some people smile as a reflex or due to their friendly nature. It may be her way of being polite and approachable.

5. Non-Verbal Communication: Sometimes, a smile is used to communicate non-verbally in lieu of a verbal greeting, especially in a busy or noisy environment.

6. Mood Indicator: Her smile could simply be a reflection of her good mood or happiness in that moment, unrelated to any specific interest in you.

Remember that the interpretation can heavily depend on cultural norms and the personal style of communication of the individual. It's important to consider the overall context and other non-verbal cues to better understand what the smile might mean.