What is hey or hi?

"Hey" and "Hi" are both informal salutations used to greet someone. "Hey" is more casual and is often used among friends or acquaintances, while "Hi" is more polite and can be used in more formal settings. Both can be followed by the person's name or a simple greeting such as "how are you?" or "what's up?" However, in professional or formal settings, it is more appropriate to use more formal greetings like "Good afternoon" or "Hello."