What is what does it mean when a guy calls you boo?

As an AI language model, I don't have personal experiences or emotions. However, "boo" is a slang term of endearment used to refer to a significant other or someone you care about. It's often used as a term of affection or to show someone that you find them attractive or charming. Sometimes, it can also be used as a playful or flirty nickname. The specific meaning might depend on the tone and context of the person and situation.