Volts

The unit of measure for electrical potential.

Basically, a volt is the ammount of force needed to push 1 amp through 1 ohm of resistance. So if you have a circuit that has a resistance of 500 ohm, and needs 10ma (1/100 of an amp) to power up, you need 5v to power it.

There is a typical misunderstanding about volts. Usually people see a "high voltage sign" and think that the volts can cause harm. Actually, what it is, is that everything has resistance, including your body. So the high voltage could push a large amount of current (amps) through you, and the amps is what does the harm, It is just the voltage that enables it.