Define power factor. On which factors does power factor depend ?

The power factor is defined as the ratio between resistance to the impedance (or)
The cosine of the phase angle ($\mathrm{\Phi }$) between voltage and current in an a.c circuit is called power factor.
The power factor cos($\mathrm{\Phi }$) = $\frac{\mathrm{R}}{\mathrm{Z}}$. So it depends on resistance (R) and impedance (Z)
where, Z depends on frequency.