What is a dipole??

As shown in the diagram below, a dipole (or known as an electric dipole) contains two separated charges, which are equal in magnitude and opposite in sign (+q and -q), and the two charges are separated in a fixed distance (r).

A polar covalent bond contains a slightly positive end (δ+) and a slightly negative end (δ-). The two ends make a dipole.

Two points should be noted :
1. All polar molecules are dipoles, but NOT all dipoles are polar molecules.
2. Molar bonds may NOT be a dipole. For example, the C-Cl bond in CCl₄ is not polar because the magnitude of positive charge on the C atom is four times of the negative charge on the Cl atom.

Dipole is used in two contexts. One would be a bond dipole and the other would be a molecular dipole.

A common example used is CCl4. The four bonds are each polar covalent bonds and each has a bond dipole in the manner hcbiochem describes. However, the entire molecule, when considered in its totality, is nonpolar, having no molecular dipole at all.

Another way to describe uneven distribution of charge is to say that the geometric center of the positive charges in the molecule (that is, the protons only) is in a different location than the geometric center of the negative charges (which are, of course, all of the electrons in the molecule).

A dipole is any imbalance in charge throughout a molecule. A molecule which is polar, like HF, has a permanent uneven distribution of charge over the molecule with the F atom being more negatively-charged and the H atom being more positively charged.