Inaudible means impossible to hear or too quiet to be heard clearly. When something is inaudible, the sound exists, but it's so faint that your ears can't pick it up.

Think about whispering a secret across a noisy cafeteria: your friend sees your lips moving but can't make out the words. Your whisper became inaudible because of the background noise. Or imagine a teacher speaking while facing the blackboard with their back to the class. Their voice might become nearly inaudible to students in the back row.

You might see this word in stage directions for plays: “The actor's final words should be inaudible to the audience.” It's also useful for describing sounds that fade away: a train whistle that starts loud but becomes inaudible as the train moves into the distance, or a dog whistle that's inaudible to human ears but perfectly clear to dogs.