RMS is a constant amount of wattage that a speaker can handle, the higher usually the better. RMS is also the constant amount of watts a amp can produce, again higher being better. The problem is that a lot of companies post pmpo(I think thats what it is called), and that is the max that it can take in, if it is a speaker, and put out if it is a amp. A speaker may be able to take a higher peak of wattage but has lower rms, this tends to mean lower quality and performance. Basic rules is the higher the rms usually the better the speaker, don't put too much on the peak input. So look for rms, don't worry about the rest.