ODNO is when you trick a ballast into thinking there are 2 or 4 bulbs hooked up to it when there is actually 1. the result is 2 or 4x the power going to the bulb. It shortens the life of the bulb considerably since it generate a lot more heat, but the light output goes up by 50% and 100% respectfully. There are many instructions on how to do this, and it only works with Electronic ballasts.