stable?

what does it mean when it says like 2 ohm stable? whats with the stable? this is on an amp by the way

im lookin for an amp thats either 150w rms 2 channel 2 ohms or monoblock 300w rms 4 ohms

The lower the impedance of the speaker you attach to the amp, the more current is drawn from the amp for a given output voltage. The amp can only handle so much current though, if you try to draw more than it can handle you'll start to blow transistors. Therefore, amps are given a minimum "stable" impedance, below which the chance of frying the amp due to excessive current draw is too great. In other words, you should be able to attach a speaker setup at or above this rated impedance and the amp won't fuss at you. If you attach a speaker setup below this rated impedance the amp will go into protection and shut off if you're lucky, or blow up if you're unlucky.