expected ionic dipole moment

The expected dipole moment of a polar molecule is the dipole moment of the molecule if it were ionic.

\ce{H-F} expected dipole moment

If $\mathrm{HF}$ were totally ionic, then expected dipole moment would be $\mathrm{electron}\mathrm{charge}\times \mathrm{H}-\mathrm{F}\mathrm{bond}\mathrm{distance}=1.47\cdot 10^{-29}\mathrm{C}\cdot \mathrm{m}=4.40\mathrm{D}$.