The correct answer is: $\frac{{{\text{Root Mean Square value}}}}{{{\text{Peak value}}}}.$
The form factor is a dimensionless quantity that is used to characterize the shape of a waveform. It is defined as the ratio of the root mean square (RMS) value of the waveform to its peak value. The RMS value is a measure of the average power of the waveform, while the peak value is the maximum value of the waveform. The form factor is important in many applications, such as power electronics and signal processing.
The other options are incorrect because they do not represent the correct definition of the form factor. Option A is the ratio of the average value to the RMS value, which is not the same as the form factor. Option B is the ratio of the average value to the peak value, which is also not the same as the form factor. Option C is the ratio of the RMS value to the average value, which is the reciprocal of the form factor.