A lot of people know the difference between video and audio because of their purposes. Video refers to what you can see. This means that the shows that you watch on television are usually in video mode because the various characters that you see are moving.
Audio refers to the sound that you will hear while you are watching the video. The audio should coincide with the video so that you will not be confused with the things that you are watching. It is also possible for the audio to be applied in other ways. For example, the songs that you hear on the radio can be heard because of proper audio.