They are calling it START and STOP. I'll call it Suspend and Un-Suspend.
Why do I call it something different than what Oracle calls it? Because it is my understanding that it really does not actually stop or stat an instance. Instead, it turns off or on access to the instance. This has a couple of implications.
1. If you really need to get your instance restarted because of a problem, This won't do it. You will still have to open an SR for it to happen
2. When you "Stop" your instance, I have been told the billing does go to $0 but to a percentage of your billing rate. I've heard both 10% and 15% but have not been able to verify what the real amount is.
3. Stop and start are instantaneous. If you STOP (Suspend) your intance, it immediately turns off access.
As I get more info I'll most likely update the post with the real percentage. Until then, this gives you an idea of what is happening.