The simple case of an electric dipole is when a positive charge and a negative charge separated by a distance
The electric dipole moment
When you have many charges, a dipole is a separation of the positive charges from the negative ones, you'll have two poles.
Here's an example :
The Oxygen is more electronegative so it'll pull the electrons toward it self, the electrons are negatively charged so you'll have a negative charge around the Oxygen
The overall electric dipole moment is the vector addition of all the electric dipole moments :
another example :