A polar bond is a bond where there is an uneven distribution of charge in the molecule, due to the ability of more electronegative atoms to attract electron pairs towards themselves which creates an electric dipole. The more electronegative atom gets a partial positive charge and the less electronegative atom gets a partial positive charge.
For a bond between two atoms to be polar, the difference in electronegativity between the two atoms should be roughly between 0.5 and 2.0. In this case, the more electronegative atom will draw the charge density towards itself to create the dipole, but not strong enough to completely strip the other atoms of electrons. The bigger the difference in electronegativity, the more polar the bond.
