How have you been?

It's asking about someone's recent health or general wellbeing.

Thanks, Mr. Wordy. So it is simply just a greeting like "how are you?"

Yes, it can be used as a general greeting, like "How are you?", without the speaker necessarily wanting or expecting a detailed, literal answer. (There's a joke that the definition of a bore is someone who "when you ask him how he is, he tells you".) It depends to some extent on how it's said. If someone says "How ya bin?" quickly and in an offhand way then it's probably a casual greeting that do