1. adjective
a) Being in a state of one of two mutually exclusive conditions such as on or off, true or false, presence or absence of a signal.
Binary states are often abstracted as 1 and 0 in computer science.
b) Concerning logic whose subject matter concerns binary states.
Two ingredients are combined in a binary poison.
2. noun
a) The bijective base-2 numeral system, which uses only the digits 0 and 1.
b) An executable computer file.
Wikipedia foundation.