A digital circuit is based on a number of discrete voltage levels, as distinct from an analog circuit that uses continuous voltages to represent variables directly. In most cases the number of voltage levels is two: one near to zero volts and one at a higher level depending on the supply voltage in use. These two levels are often represented as "Low" and "High."
Digital circuits are the most common mechanical representation of Boolean algebra and are the basis of all digital computers. They can also be used to process digital information without being connected up as a computer. Such circuits are referred to as "random logic".