We're talkin about a polar molecule when the center of gravity of its negative charges is different from the center of gravity of its positive charges. The most famous example of a polar molecule is H20
(NB: the dots are only here for the simplicity, don't pay attention to them)
On this very schematic drawing, you can see that the center of gravity of the (partial)positive charges is located on the Hydrogen atom whereas the center of gravity of the negative charges is located half way between the 2 oxygen atoms.
On the other side, a non polar molecule, such as CO2 (see below)
(-)O=C(+)=O(-)
has the center of gravity of both its negative and positive charges at the same place, i.e. on the carbon atom.
For the economic size, I won't be able to halp ya, sorry, I'm just a scientist, However, the polarity of a molecule is of great interest in a lot of domain (dielectrics, solvents)