Ohms is a measurement of resistance. The higher the ohm the higher the resistance on the electrical circuit. The higher the resistance, the less power the amplifier will be able to supply. For example, if an amplifier outputs 500 watts at 8 ohms, it will output 1000 watts at 4 ohms, and 250 watts at 16 ohms. Pretty simple, right? So now you may be thinking, why not just buy some small amplifier, and then get as low of a resistance as possible on it to get lots of wattage from it. The problem is, amplifiers are only stable to a certain impedance. Most class A/B amps are only stable down to 2ohms, while class D's are usually stable down to 1ohm. There are exceptions to this of course, but the point is you cant simply keep getting more and more power from an amplifier, forever, by decreasing the ohm load on it. Otherwise we'd all be running some tiny amp at .00001 ohms.
Hope that helps.
