In dielectrics, polarization refers to the alignment of dipoles within a material under the influence of an external electric field. It is defined as the dipole moment per unit volume of the material. The dipole moment is a measure of the separation of positive and negative charges in a molecule or material.
Thus, polarization \( P \) is given by:
\[
P = \frac{\text{Dipole moment}}{\text{Volume}}
\]
Therefore, the correct answer is (C), as polarization is the dipole moment per unit volume.