An ohm is a unit of measure of the resistance of an electric circuit.
A watt is a unit of electric power.

So if you are in your swimming pool and you try to kick your girlfriend in the butt and knock her down it will take a lot more power in your leg to do it than if you done the same thing on the deck of the pool. Therefore it takes a lot more power under water to get the same reaction than it does in air because there is more resistance. So it is with your speakers. A speaker of 8 ohms has much more resistance than a speaker of 4 ohms. Therefor it takes more power to get the same noise out of a speaker of less resistance. There are formulas that will give you precise answers of watts, ohms and all that if you are really interested. Just keep in mind, if your going to punch a guy in the nose, better check your watts of power in your biceps against his ohms of resistance to your watts of power.

Taken from the wisdom of Grandpa Doug. I know Uncle Dave could do a better job of explaining, but after all, I’m getting old and he aint married to Ruthie.