When a dielectric is placed in an electric field, the dipoles align along the field direction. This effect is called polarization, which is the dipole moment per unit volume. Consider a long string of aligned dipoles with uniform dipole moments. The equal and opposite charges in adjacent dipoles cancel each other, leaving net negative and positive charges at the dielectric surface, called surface-bound charges. The surface-bound charge density is the charge per unit area. Using the definition of the dipole moment, the charge can be expressed in terms of polarization. For an oblique surface, this charge is distributed over an extended area. Defining a normal to this area gives the expression for surface-bound charge density. When the polarization is non-uniform, the alignment of dipoles accumulates charges inside the dielectric, leading to volume-bound charges that are equal and opposite to the surface-bound charges. The potential created by a polarized dielectric at a field point can be estimated solely from these bound charges and is the sum of the potentials produced by the surface and volume-bound charges.