What is a binary decision variable?

I know thats it can be either a 0 or 1, but how is it defined?|||Binary means two. It is any variable or decision point that has exactly two possible outcomes. These are commonly exressed as 0 and 1, or could be expressed as yes or no, on or off. There is a decision tree diagram in the reference below which shows several such biranry decision points.|||A variable that can be either true of false. Like a bool in C++