Is there any usage difference between "hi" and "hello"?
No, there really isn't a difference between "hi" and "hello." They both are used as a greeting. "Hello" is a little more formal but it can be used around people you don't know and to your friends as well. The same thing applies with "hi." You can use "hi" in formal and informal situations as well. Ex: Hi mom! How are you? Ex: Hello! My name is Becca. Ex: Hello dear. It's been too long since I've seen you. Ex: Hi there, I'm calling about my eye appointment next week. I need to reschedule.