1. in computing, a variable that can take only the values of zero or one. [bi(nary) + (digi)t]

2. in information theory, the quantity of information that decreases uncertainty or the germane alternatives of a problem by one half. For example, if a dollar bill has been placed in one of 16 identical books standing side by side on a shelf, and one has to identify this book by asking a minimum number of questions that can be answered only by “yes” or “no,” the best way to begin would be to ask if the book is to the right (or to the left) of center. The answer to this question would provide one bit of information.