Ohms are a unit of measurement. Like inchs or meters. They are used ot measure impeadence (resistence)of an electrical curcuit. A sub(s)wired at 8 ohms has a greater resistance than a sub(s) wired at 2 ohms. Therefore the amp is able to push more power into less restrictive loads. ALL amps have a stable range of impedences in which they can be safley operated.