A dipole is a system which has an overall neutral
charge but where the electrostatic charges are so distributed such that one area is more negative
and another more positive
. The strength of this effect, and so the dipole, is referred to as the dipole moment
. An item that has a dipole is referred to as polar
The water molecule has a significant dipole as the oxygen molecule is significantly more negative than the hydrogens and they are not all in a line. If the water molecule were linear (like carbon dioxide) then it would not have an overall dipole. This is important as the semi-ionic nature of water is why it is a liquid at room temperature.
Dipole is also the name for a particular form of aerial
involving two rods
which are almost touching, arranged like a single rod with a small piece removed from the middle.