An auditory hallucination is when you hear things that aren't really there. Just like when you pretend to hear a phone ringing or your mommy calling your name when she isn't actually calling you. But with an auditory hallucination, you really hear the sound, but it's not something that other people can hear.
It's like when you're dreaming and you hear a sound that isn't really there, but with an auditory hallucination, you are awake and it feels like it's happening in real life.
Some people might hear voices speaking to them, while others might hear strange noises or music. It's important to tell a grown-up if this happens to you, because they can help you figure out why it's happening and how to make it stop if needed.