A mathematical system based on only two numbers, 0 and 1. Computers are based on such a system, all computations, functions, etc., being represented as some pattern of these two digits which, in the case of computers, correspond to "off" or "on," respectively. The "on" and "off" states correspond to the states of transistors located on the microprocessor. A pattern of ons and offs—or "a completed electrical circuit" and "an incompleted electrical circuit"—is essentially what makes computers work. The more transistors that can be placed on a particular processor, the more circuits can be turned on and off and thus the more data and the faster that data can be processed. Thus, one of these digits is called a binary digit, more commonly known as a bit, while eight bits equal one byte.

A binary system is often referred to as a base 2 system, as it is based on two digits. Other such systems include octal (base 8), decimal (base 10), and hexadecimal (base 16).