What is what does it mean when a girl says heyy?

As an AI language model, I can give you some general information about what it might mean when a girl says "heyy," but it's important to remember that everyone communicates differently and there's no 100% accurate way to interpret any message. In general, however, "heyy" can be seen as a friendly greeting - it's a way of saying "hello" that's a little more informal and playful than a typical greeting. Depending on the context, it could also be an attempt to start a conversation or express interest in someone. But again, it's important to take each situation on a case-by-case basis and not assume too much from a single word!