Main point: This is something for headphones only, not for headsets.
We have nothing to do with OHMs and really don't know too much about them. If you need to knwo more, you should to speak with an audio professional (not necessarily an audiologist but maybe an audio store/center or a DJ supply store.
Short answer: The Ohm is a unit that measures the resistance in an electrical current. For our department, it has to do with the power distribution to the headphones. The lower the OHMs means the amplifier needs a higher current outpout. Higher means that the amplifier needs a higher voltage swing.
Confusing? Heck ya. Look at that graph. Oh My!
Yeah, don't worry about it.