The adverb audibly describes something that's loud enough for you to hear it. If people are whispering audibly in a movie theater, it means you can hear them, and you might want to find a new seat.
When you sneeze audibly during a ballet performance, people can hear you. If you whisper audibly to your best friend that you'll meet her after the lecture's over, she can hear what you're saying. Audibly comes from the adjective audible, which is rooted in the Latin audire, "to hear."