Something that can be broken into two categories is binary. Binary means something close to dual or double.
You can remember what binary means if you know that bi- means two. Black and white are often set up as a binary, as are light and dark and good and evil. One binary we see all the time is the male and female symbols you see on bathroom doors. In computing, binary is a code of zeros and ones (computer programming) also known as base two. A binary is also a double star — two stars revolving around each other.