Nonuniform charge distribution along a whole molecule determines existence of an electric multipole in it (dipole, quadrupole, octupole, etc.)

Dipole is an atom or molecule, whose net charge is equal to zero, but it still has electric field, because the centre of its positive charge does not coincide with the center of the negative charge. In other words, the electric dipole is an assemblage of two point electric charges, which are situated at some distance from each other, they are equal in value and opposite in sign. Dipole is characterized by dipole moment.An ion can be a dipole at the same time, if numbers of protons and electrons in it do not coincide, and centers of the positive and the negative charge do not coincide either.

A dipole can be constant, when charge separation appears because the configuration of its elements is fixed. Dipole can be induced (or, temporary). It is formed, when a nonpolar atom or molecule happens in the zone of action of an ion or a dipole.

Interactions between dipoles are called dipole-dipole (van der Waals) interactions.