Tyler, this is probably more than you wanted to know:
RMS stands for Root Mean Squared. If you think about it, a sine wave fluctuates between some positive voltage and some negative voltage evenly. Assuming it is centered around 0 volts, if you took the average voltage it would always be zero because the wave is the same above and below the line. (assume it is 1 volt at peak, the wave would start at 0, then 1, then then 0, then -1, then 0, etc. Take the average of that and you get 0.)
But in real life, when the wave is producing a negative voltage it is not sucking energy back out of the room, it is just producing energy in a different direction (that's not quite true but the simplest way I can explain it.)
So to get the average voltage that makes sense in reality, you square everything (the roots) first (making them all positive numbers), then you take the average (or mean) of those, then you take the square root of that. And you end up with the Root Mean Squared, which is a real measure of the average energy that the sine wave carried.
This is why voltages in electronics are talked about in terms of RMS and peak. RMS is basically a measure of the average and peak is the peak of course.
I don't know if that made enough sense to you yet, but when you get to physics pay attention! It's actually pretty interesting.
Good luck.
Pete, the nerdy mechanical engineer.