binary opposition, the principle of contrast between two mutually exclusive terms: on/off, up/down, left/right etc; an important concept of structuralism, which sees such distinctions as fundamental to all language and thought. The theory of phonology developed by Roman Jakobson uses the concept of ‘binary features’, which are properties either present or absent in any phoneme: voicing, for example is present in /z/ but not in /s/. This concept has been extended to anthropology by Claude Lévi‐Strauss (in such oppositions as nature/culture, raw/cooked, inedible/edible)
Basically, it means that a situation is reducable to two possible answers or states. . for instance, alive or dead Warm or cold Day or night Good or bad yes or no
These may not be the best explanations, but any situation (philosophically) that has two and only two possible outcomes. . . no shade of Grey.