Permanent dipoles: These occur when two atoms in a molecule have substantially different electro negativity: One atom attracts electrons more than another, becoming more negative, while the other atom becomes more positive.
Instantaneous dipoles: These occur due to chance when electrons happen to be more concentrated in one place than another in a molecule, creating a temporary dipole.
Induced dipoles: These can occur when one molecule with a permanent dipole repels another molecule's electrons, inducing a dipole moment in that molecule.
A molecule is polarized when it carries an induced dipole.
For more information: https://en.wikipedia.org/wiki/Dipole#Molecular_dipoles