RMS

“Root Mean Square”
Basically the area under a curve divided by the time it lasts for, this is represented as the integral over an area divided by its duration (1/T) which is the average.

The integral in this case ranges from $t_1$ to $t_1$+T $I_{rms}=I=\sqrt{\frac{1}{T}\int i^2}\left(t\right)dt$
$V_{rms}=V=\sqrt{\frac{1}{T}\int v^2}\left(t\right)dt$
Or in Sinusoidal Waveforms
$I=\frac{I_{peak}}{\sqrt{2}}$
$V=\frac{V_{peak}}{\sqrt{2}}$
Ohms Law
$V=ZI$