DC (VOLTAGE)

The term DC when used in terms of a voltage, means "Direct Current".  This means that the voltage always stays the same, and it is therefore very different fro AC voltage where AC voltage is constantly varying.  A good example of a DC voltage is the voltage we receive from batteries - the type AA, AAA, C or D type we use all of the time, or even our car batteries.  A small type battery such as an AA, AAA, C or D type normally is a constant voltage of about 1.5 volts.  A car battery is said to be 12 volts, but actually the average DC voltage is about 13.7 volts DC.  A car battery's voltage does try and stay constant, however, its value will depend on both the charge that it has and also how much current it must supply to the car and to accessories.  A car battery will therefore vary somewhat between about 10.96 volts and 16.44 volts, with the average about 13.7 volts.

So a battery is a good example of a DC voltage.  House current is almost always AC voltage and not DC voltage.  Power companies long ago found that it was less expensive to supply AC voltage to houses and businesses.