The ratio of the maximum value of an alternating signal to its RMS value is known as its: 

Crest Factor

The crest factor is the ratio of the maximum value to the R.M.S value of an alternating quantity.

\(Crest \space Factor={Maximum \space value\over RMS \space value}\)

Form Factor

The form factor is the ratio of the RMS value to the average value of an alternating quantity.

\(Form \space Factor={RMS \space value\over Average \space value}\)

Pitch factor

It is the ratio of the resultant EMF of the short-pitched coil to the resulting EMF of the full-pitched coil.

\(K_p=cos({\alpha \over 2})\)

Distribution factor

Kd = Distribution factor = \({sin({m\beta\over 2})\over m \space sin({\beta \over 2})}\)