Cycles is an audiovisual composition. When you launch Cycles, you can view a performance of the piece. If you let it run, it will create a new performance, then another, infinitely; these are completely different generations of the piece. This is because Cycles is procedurally generated, every time (like a Minecraft world). Each generation is related, and may sound kind of similar, but might sound totally different.
There are billions of possible generations - you don't have to watch every one, of course, but it's nice to think that the one you're watching has probably never been seen by anyone else.