Polarized outlets are different in that the slot for the neutral wire is wider than the slot for the hot wire. This makes it difficult to insert the electrical plug the wrong way, although I wouldn't put it past some people. The purpose for this is most easily seen in devices such as toasters and lamps, which have exposed parts that can have electrical current running through them. A lamp, for example, powers the bulb both through a button on the bottom and the body of the screw the light bulb fits into. Since the screw fitting is large and easy to accidentally touch, in a properly wired polarized outlet, the screw fitting will be connected to the neutral wire. This is much safer because the neutral conductor, also called the grounded conductor, should always be at zero volts with respect to the idiot changing the light bulb without turning off the power first. This makes it much less likely to deliver an electrical shock.
Polarized, non-grounded outlets are becoming increasingly rare these days.
