Two specific, mutually exclusive states, e.g. yes/no, correct/incorrect, on/off, O/ L or 0/1.
The binary numerical system has the base 2. With n binary signals it is possible to define 2n states. Therefore, e.g., with n = 8 = 28 there are 256 possible states.
Binary technology forms the basis for the principle of operation of computers. For this reason all entries in a computer must represented in a binary code.