A dipole refers to a bond in which its two ends have opposite charges. A dipole results from a large difference in electronegativity between two atoms in a bond.
For instance, consider the bond between hydrogen and chlorine in HCl. The electronegativity of hydrogen is 2.2 while that of chlorine is 3.16. The significant electronegativity difference between the two atoms leads to a charge separation.
A partial positive charge appears on the atom that is less electronegative (hydrogen) while a negative charge appears on the more electronegative atom (chlorine).
This charge separation occurs because the shared electrons of the bond are more closely attracted to chlorine making it partially negative compared to hydrogen. A dipole moment now exists in the H-Cl bond hence the molecule is said to have a dipole.
