What is Bond dipole, dipole moment?

In a bond between atoms of different electronegativities the electrons lean towards the more electronegative atom, which bears a partial charge $-\delta e$ while its partner bears $+\delta e$ ($0 < \delta < 1$). The bond dipole is the vector $\vec\mu = \delta e\, \vec d$, of norm $\delta e d$, pointing from the negative to the positive partial charge, $\vec d$ being the vector between them. The dipole moment of a molecule is the vector sum of its bond dipoles (and of the contributions of its lone pairs); it is expressed in coulomb metres or in debyes, $1\,\mathrm{D} = 3.336 \times 10^{-30}\,\mathrm{C}\,\mathrm{m}$. A molecule with a non-zero dipole moment is a polar molecule.