An electric dipole consists of two equal and opposite charges, -q and +q, separated by a very small distance 2a.
Although in an electric dipole the two charges are equal and opposite, giving a zero net charge, the fact that they are slightly displaced is enough to produce a non-vanishing electric field. In many substances, like H2O, the centres of the positive and the negative charges of the molecules are slightly separated and these resemble electric dipoles.
